diff --git a/api/soap/mc_api.php b/api/soap/mc_api.php
index 9732f90714..6460f3a26e 100644
--- a/api/soap/mc_api.php
+++ b/api/soap/mc_api.php
@@ -31,6 +31,7 @@
 
 require_api( 'api_token_api.php' );
 
+use Mantis\Exceptions\ClientException;
 use Mantis\Exceptions\LegacyApiFaultException;
 
 /**
@@ -287,12 +288,17 @@ static function faultFromException( Exception $p_exception ) {
 	 * @param stdClass|array $p_object Object.
 	 * @return array
 	 */
-	static function objectToArray($p_object ) {
-		if( is_object( $p_object ) ) {
-			return get_object_vars( $p_object );
+	static function objectToArray( $p_object, $p_recursive = false ) {
+		$t_object = is_object( $p_object ) ? get_object_vars( $p_object ) : $p_object;
+		if( $p_recursive && is_array( $t_object ) ) {
+			foreach( $t_object as $t_key => $t_value ) {
+				if( is_object( $t_object[$t_key] ) || is_array( $t_object[$t_key] ) ) {
+					$t_object[$t_key] = ApiObjectFactory::objectToArray( $t_object[$t_key], $p_recursive );
+				}
+			}
 		}
 
-		return $p_object;
+		return $t_object;
 	}
 
 	/**
@@ -353,7 +359,7 @@ static function isFault( $p_maybe_fault ) {
 	 */
 	static function throwIfFault( $p_maybe_fault ) {
 		if( ApiObjectFactory::isFault( $p_maybe_fault ) ) {
-			throw new LegacyApiFaultException( $p_maybe_fault->fault_string, $p_maybe_fault->status_code );
+			throw new LegacyApiFaultException( $p_maybe_fault->getMessage(), $p_maybe_fault->getCode() );
 		}
 	}
 }
@@ -876,9 +882,10 @@ function mci_get_version( $p_version, $p_project_id ) {
  *
  * @param string|object $p_version The version string or object with name or id or both.
  * @param int $p_project_id The project id.
+ * @param string $p_field_name Version field name (e.g. version, target_version, fixed_in_version)
  * @return int|RestFault|SoapFault The version id, 0 if not supplied.
  */
-function mci_get_version_id( $p_version, $p_project_id ) {
+function mci_get_version_id( $p_version, $p_project_id, $p_field_name = 'version' ) {
 	$t_version_id = 0;
 	$t_version_for_error = '';
 
@@ -903,7 +910,11 @@ function mci_get_version_id( $p_version, $p_project_id ) {
 		$t_error_when_version_not_found = config_get( 'webservice_error_when_version_not_found' );
 		if( $t_error_when_version_not_found == ON ) {
 			$t_project_name = project_get_name( $p_project_id );
-			return ApiObjectFactory::faultBadRequest( "Version '$t_version_for_error' does not exist in project '$t_project_name'." );
+			throw new ClientException(
+				"Version '$t_version_for_error' does not exist in project '$t_project_name'.",
+				ERROR_INVALID_FIELD_VALUE,
+				array( 'version' )
+			);
 		}
 
 		$t_version_when_not_found = config_get( 'webservice_version_when_not_found' );
@@ -983,7 +994,11 @@ function mci_get_category_id( $p_category, $p_project_id ) {
 	$t_category_id = $fn_get_category_id_internal( $p_category, $p_project_id );
 	if( $t_category_id == 0 && !config_get( 'allow_no_category' ) ) {
 		if( !isset( $p_category ) ) {
-			return ApiObjectFactory::faultBadRequest( 'Category field must be supplied.' );
+			throw new ClientException(
+				'Category field must be supplied.',
+				ERROR_EMPTY_FIELD,
+				array( 'category' )
+			);
 		}
 
 		# category may be a string, array with id, array with name, or array
diff --git a/api/soap/mc_issue_api.php b/api/soap/mc_issue_api.php
index 8dd95cc148..57e614048d 100644
--- a/api/soap/mc_issue_api.php
+++ b/api/soap/mc_issue_api.php
@@ -906,228 +906,14 @@ function mc_issue_add( $p_username, $p_password, $p_issue ) {
 		return mci_fault_login_failed();
 	}
 
-	if( is_object( $p_issue ) ) {
-		$p_issue = ApiObjectFactory::objectToArray( $p_issue );
-	}
-
-	if( !isset( $p_issue['summary'] ) )  {
-		return ApiObjectFactory::faultBadRequest( 'Summary not specified' );
-	}
-
-	if( !isset( $p_issue['description'] ) )  {
-		return ApiObjectFactory::faultBadRequest( 'Description not specified' );
-	}
-
-	if( !isset( $p_issue['project'] ) )  {
-		return ApiObjectFactory::faultBadRequest( 'Project not specified' );
-	}
-
-	$t_project = $p_issue['project'];
-
-	$t_project_id = mci_get_project_id( $t_project );
-	$g_project_override = $t_project_id; # ensure that helper_get_current_project() calls resolve to this project id
-
-	if( !mci_has_readwrite_access( $t_user_id, $t_project_id ) ) {
-		return mci_fault_access_denied( $t_user_id );
-	}
-
-	$t_handler_id = isset( $p_issue['handler'] ) ? mci_get_user_id( $p_issue['handler'] ) : 0;
-	$t_priority_id = isset( $p_issue['priority'] ) ? mci_get_priority_id( $p_issue['priority'] ) : config_get( 'default_bug_priority' );
-	$t_severity_id = isset( $p_issue['severity'] ) ?  mci_get_severity_id( $p_issue['severity'] ) : config_get( 'default_bug_severity' );
-	$t_status_id = isset( $p_issue['status'] ) ? mci_get_status_id( $p_issue['status'] ) : config_get( 'bug_submit_status' );
-	$t_reproducibility_id = isset( $p_issue['reproducibility'] ) ?  mci_get_reproducibility_id( $p_issue['reproducibility'] ) : config_get( 'default_bug_reproducibility' );
-	$t_resolution_id =  isset( $p_issue['resolution'] ) ? mci_get_resolution_id( $p_issue['resolution'] ) : config_get( 'default_bug_resolution' );
-	$t_projection_id = isset( $p_issue['projection'] ) ? mci_get_projection_id( $p_issue['projection'] ) : config_get( 'default_bug_resolution' );
-	$t_eta_id = isset( $p_issue['eta'] ) ? mci_get_eta_id( $p_issue['eta'] ) : config_get( 'default_bug_eta' );
-	$t_view_state_id = isset( $p_issue['view_state'] ) ?  mci_get_view_state_id( $p_issue['view_state'] ) : config_get( 'default_bug_view_status' );
-	$t_summary = $p_issue['summary'];
-	$t_description = $p_issue['description'];
-	$t_notes = isset( $p_issue['notes'] ) ? $p_issue['notes'] : array();
-
-	# TODO: #17777: Add test case for mc_issue_add() and mc_issue_note_add() reporter override
-	if( isset( $p_issue['reporter'] ) ) {
-		$t_reporter_id = mci_get_user_id( $p_issue['reporter'] );
-
-		if( $t_reporter_id != $t_user_id ) {
-			# Make sure that active user has access level required to specify a different reporter.
-			$t_specify_reporter_access_level = config_get( 'webservice_specify_reporter_on_add_access_level_threshold' );
-			if( !access_has_project_level( $t_specify_reporter_access_level, $t_project_id, $t_user_id ) ) {
-				return mci_fault_access_denied( $t_user_id, 'Active user does not have access level required to specify a different issue reporter' );
-			}
-		}
-	} else {
-		$t_reporter_id = $t_user_id;
-	}
-
-	if( ( $t_project_id == 0 ) || !project_exists( $t_project_id ) ) {
-		if( $t_project_id != 0 ) {
-			return ApiObjectFactory::faultNotFound( "Project '" . $t_project->name . "' does not exist." );
-		}
-
-		return ApiObjectFactory::faultNotFound( "Project with id '" . $t_project_id . "' does not exist." );
-	}
-
-	if( !access_has_project_level( config_get( 'report_bug_threshold' ), $t_project_id, $t_user_id ) ) {
-		return mci_fault_access_denied( $t_user_id, 'User does not have access right to report issues' );
-	}
-
-	$t_access_check_result = mci_issue_handler_access_check( $t_user_id, $t_project_id, /* old */ 0, /* new */ $t_handler_id );
-	if( $t_access_check_result !== true ) {
-		return $t_access_check_result;
-	}
-
-	$t_category = isset( $p_issue['category'] ) ? $p_issue['category'] : null;
-
-	$t_category_id = mci_get_category_id( $t_category, $t_project_id );
-	if( ApiObjectFactory::isFault( $t_category_id ) ) {
-		return $t_category_id;
-	}
-
-	$t_version_id = isset( $p_issue['version'] ) ? mci_get_version_id( $p_issue['version'], $t_project_id ) : 0;
-	if( ApiObjectFactory::isFault( $t_version_id ) ) {
-		return $t_version_id;
-	}
-
-	$t_fixed_in_version_id = isset( $p_issue['fixed_in_version'] ) ? mci_get_version_id( $p_issue['fixed_in_version'], $t_project_id ) : 0;
-	if( ApiObjectFactory::isFault( $t_fixed_in_version_id ) ) {
-		return $t_fixed_in_version_id;
-	}
-
-	$t_target_version_id = isset( $p_issue['target_version'] ) ? mci_get_version_id( $p_issue['target_version'], $t_project_id ) : 0;
-	if( ApiObjectFactory::isFault( $t_target_version_id ) ) {
-		return $t_target_version_id;
-	}
-
-	if( is_blank( $t_summary ) ) {
-		return ApiObjectFactory::faultBadRequest( 'Mandatory field \'summary\' is missing.' );
-	}
-
-	if( is_blank( $t_description ) ) {
-		return ApiObjectFactory::faultBadRequest( 'Mandatory field \'description\' is missing.' );
-	}
-
-	$t_bug_data = new BugData;
-	$t_bug_data->profile_id = 0;
-	$t_bug_data->project_id = $t_project_id;
-	$t_bug_data->reporter_id = $t_reporter_id;
-	$t_bug_data->handler_id = $t_handler_id;
-	$t_bug_data->priority = $t_priority_id;
-	$t_bug_data->severity = $t_severity_id;
-	$t_bug_data->reproducibility = $t_reproducibility_id;
-	$t_bug_data->status = $t_status_id;
-	$t_bug_data->resolution = $t_resolution_id;
-	$t_bug_data->projection = $t_projection_id;
-	$t_bug_data->category_id = $t_category_id;
-	$t_bug_data->date_submitted = isset( $p_issue['date_submitted'] ) ? strtotime( $p_issue['date_submitted'] ) : '';
-	$t_bug_data->last_updated = isset( $p_issue['last_updated'] ) ? strtotime( $p_issue['last_updated'] ) : '';
-	$t_bug_data->eta = $t_eta_id;
-	$t_bug_data->profile_id = isset( $p_issue['profile_id'] ) ? $p_issue['profile_id'] : 0;
-	$t_bug_data->os = isset( $p_issue['os'] ) ? $p_issue['os'] : '';
-	$t_bug_data->os_build = isset( $p_issue['os_build'] ) ? $p_issue['os_build'] : '';
-	$t_bug_data->platform = isset( $p_issue['platform'] ) ? $p_issue['platform'] : '';
-
-	if( $t_version_id != 0 ) {
-		$t_bug_data->version = version_get_field( $t_version_id, 'version' );
-	}
-
-	if( $t_fixed_in_version_id != 0 ) {
-		$t_bug_data->fixed_in_version = version_get_field( $t_fixed_in_version_id, 'version' );
-	}
-
-	if( $t_target_version_id != 0 && access_has_project_level( config_get( 'roadmap_update_threshold' ), $t_bug_data->project_id, $t_user_id ) ) {
-		$t_bug_data->target_version = version_get_field( $t_target_version_id, 'version' );
-	}
-
-	$t_bug_data->build = isset( $p_issue['build'] ) ? $p_issue['build'] : '';
-	$t_bug_data->view_state = $t_view_state_id;
-	$t_bug_data->summary = $t_summary;
-	$t_bug_data->sponsorship_total = isset( $p_issue['sponsorship_total'] ) ? $p_issue['sponsorship_total'] : 0;
-	if( isset( $p_issue['sticky'] ) &&
-		 access_has_project_level( config_get( 'set_bug_sticky_threshold', null, null, $t_project_id ), $t_project_id ) ) {
-		$t_bug_data->sticky = $p_issue['sticky'];
-	}
-
-	if( isset( $p_issue['due_date'] ) &&
-		access_has_project_level( config_get( 'due_date_update_threshold' ), $t_bug_data->project_id ) ) {
-		$t_bug_data->due_date = strtotime( $p_issue['due_date'] );
-	} else {
-		$t_bug_data->due_date = date_get_null();
-	}
-
-	# omitted:
-	# var $bug_text_id
-	# $t_bug_data->profile_id;
-	# extended info
-	$t_bug_data->description = $t_description;
-	$t_bug_data->steps_to_reproduce = isset( $p_issue['steps_to_reproduce'] ) ? $p_issue['steps_to_reproduce'] : '';
-	$t_bug_data->additional_information = isset( $p_issue['additional_information'] ) ? $p_issue['additional_information'] : '';
-
-	# submit the issue
-	$t_issue_id = $t_bug_data->create();
-	$t_bug_data->process_mentions();
-
-	log_event( LOG_WEBSERVICE, 'created new issue id \'' . $t_issue_id . '\'' );
-
-	$t_cf_result = mci_project_custom_fields_validate( $t_project_id, $p_issue['custom_fields'] );
-	if( ApiObjectFactory::isFault( $t_cf_result ) ) {
-		return $t_cf_result;
-	}
-
-	$t_set_custom_field_error = mci_issue_set_custom_fields( $t_issue_id, $p_issue['custom_fields'], false );
-	if( $t_set_custom_field_error != null ) {
-		return $t_set_custom_field_error;
-	}
-
-	if( isset( $p_issue['monitors'] ) ) {
-		mci_issue_set_monitors( $t_issue_id, $t_user_id, $p_issue['monitors'] );
-	}
-
-	if( isset( $t_notes ) && is_array( $t_notes ) ) {
-		foreach( $t_notes as $t_note ) {
-			$t_note = ApiObjectFactory::objectToArray( $t_note );
-
-			if( isset( $t_note['view_state'] ) ) {
-				$t_view_state = $t_note['view_state'];
-			} else {
-				$t_view_state = config_get( 'default_bugnote_view_status' );
-			}
-
-			$t_note_type = isset( $t_note['note_type'] ) ? (int)$t_note['note_type'] : BUGNOTE;
-			$t_note_attr = isset( $t_note['note_type'] ) ? $t_note['note_attr'] : '';
-
-			$t_view_state_id = mci_get_enum_id_from_objectref( 'view_state', $t_view_state );
-			$t_note_id = bugnote_add(
-				$t_issue_id,
-				$t_note['text'],
-				mci_get_time_tracking_from_note( $t_issue_id, $t_note ),
-				$t_view_state_id == VS_PRIVATE,
-				$t_note_type,
-				$t_note_attr,
-				$t_user_id,
-				false ); # don't send mail
-
-			bugnote_process_mentions( $t_issue_id, $t_note_id, $t_note['text'] );
-
-			log_event( LOG_WEBSERVICE, 'bugnote id \'' . $t_note_id . '\' added to issue \'' . $t_issue_id . '\'' );
-		}
-	}
-
-	if( isset( $p_issue['tags'] ) && is_array( $p_issue['tags'] ) ) {
-		$t_tags_result = mci_tag_set_for_issue( $t_issue_id, $p_issue['tags'], $t_user_id );
-		if( ApiObjectFactory::isFault( $t_tags_result ) ) {
-			return $t_tags_result;
-		}
-	}
-
-	email_bug_added( $t_issue_id );
-
-	if( $t_bug_data->status != config_get( 'bug_submit_status' ) ) {
-		history_log_event( $t_issue_id, 'status', config_get( 'bug_submit_status' ) );
-	}
+	$t_issue = ApiObjectFactory::objectToArray( $p_issue, /* recursive */ true );
+	$t_data = array(
+		'payload' => array( 'issue' => $t_issue )
+	);
 
-	if( $t_bug_data->resolution != config_get( 'default_bug_resolution' ) ) {
-		history_log_event( $t_issue_id, 'resolution', config_get( 'default_bug_resolution' ) );
-	}
+	$t_command = new IssueAddCommand( $t_data );
+	$t_result = $t_command->execute();
+	$t_issue_id = (int)$t_result['issue_id'];
 
 	return $t_issue_id;
 }
diff --git a/api/soap/mc_project_api.php b/api/soap/mc_project_api.php
index 9f9f62580f..440c3a8d50 100644
--- a/api/soap/mc_project_api.php
+++ b/api/soap/mc_project_api.php
@@ -23,6 +23,8 @@
  * @link http://www.mantisbt.org
  */
 
+use Mantis\Exceptions\ClientException;
+
 /**
  * Use a standard filter to get issues associated with the specified user.
  *
@@ -675,13 +677,19 @@ function mci_project_custom_fields_validate( $p_project_id, &$p_custom_fields )
 			$t_custom_field = ApiObjectFactory::objectToArray( $t_custom_field );
 
 			if( !isset( $t_custom_field['value'] ) ) {
-				$t_error = 'Custom field has no value specified.';
-				return ApiObjectFactory::faultBadRequest( $t_error );
+				throw new ClientException(
+					'Custom field has no value specified.',
+					ERROR_EMPTY_FIELD,
+					"custom_field['value']"
+				);
 			}
 
 			if( !isset( $t_custom_field['field'] ) ) {
-				$t_error = 'Custom field with no specified id or name.';
-				return ApiObjectFactory::faultBadRequest( $t_error );
+				throw new ClientException(
+					'Custom field with no specified id or name.',
+					ERROR_EMPTY_FIELD,
+					"custom_field['field']"
+				);
 			}
 
 			$t_custom_field['field'] = ApiObjectFactory::objectToArray( $t_custom_field['field'] );
@@ -698,8 +706,11 @@ function mci_project_custom_fields_validate( $p_project_id, &$p_custom_fields )
 				continue;
 			}
 
-			$t_error = 'Custom field with no specified id or name.';
-			return ApiObjectFactory::faultBadRequest( $t_error );
+			throw new ClientException(
+				'Custom field with no specified id or name.',
+				ERROR_EMPTY_FIELD,
+				"custom_field['field']['id']"
+			);
 		}
 	}
 
@@ -717,15 +728,21 @@ function mci_project_custom_fields_validate( $p_project_id, &$p_custom_fields )
 		if( $t_def['require_report'] ) {
 			if( !isset( $t_custom_field_values[$t_name] ) ||
 			    is_blank( $t_custom_field_values[$t_name] ) ) {
-				$t_error = "Mandatory field '$t_name' is missing.";
-				return ApiObjectFactory::faultBadRequest( $t_error );
+				throw new ClientException(
+					"Mandatory field '$t_name' is missing.",
+					ERROR_EMPTY_FIELD,
+					array( $t_name )
+				);
 			}
 		}
 
 		if( isset( $t_custom_field_values[$t_name] ) &&
 		    !custom_field_validate( $t_custom_field_id, $t_custom_field_values[$t_name] ) ) {
-			$t_error = "Invalid custom field '$t_name' value.";
-			return ApiObjectFactory::faultBadRequest( $t_error );
+			throw new ClientException(
+				"Invalid custom field '$t_name' value.",
+				ERROR_EMPTY_FIELD,
+				array( $t_name )
+			);
 		}
 	}
 
diff --git a/core/commands/IssueAddCommand.php b/core/commands/IssueAddCommand.php
index c7ac0cb9b1..782ff1a43e 100644
--- a/core/commands/IssueAddCommand.php
+++ b/core/commands/IssueAddCommand.php
@@ -205,16 +205,9 @@ function validate() {
 
 		$t_category = isset( $t_issue['category'] ) ? $t_issue['category'] : null;
 		$t_category_id = mci_get_category_id( $t_category, $t_project_id );
-		ApiObjectFactory::throwIfFault( $t_category_id );
-
-		$t_version_id = isset( $t_issue['version'] ) ? mci_get_version_id( $t_issue['version'], $t_project_id ) : 0;
-		ApiObjectFactory::throwIfFault( $t_version_id );
-
-		$t_fixed_in_version_id = isset( $t_issue['fixed_in_version'] ) ? mci_get_version_id( $t_issue['fixed_in_version'], $t_project_id ) : 0;
-		ApiObjectFactory::throwIfFault( $t_fixed_in_version_id );
-
-		$t_target_version_id = isset( $t_issue['target_version'] ) ? mci_get_version_id( $t_issue['target_version'], $t_project_id ) : 0;
-		ApiObjectFactory::throwIfFault( $t_target_version_id );
+		$t_version_id = isset( $t_issue['version'] ) ? mci_get_version_id( $t_issue['version'], $t_project_id, 'version' ) : 0;
+		$t_fixed_in_version_id = isset( $t_issue['fixed_in_version'] ) ? mci_get_version_id( $t_issue['fixed_in_version'], $t_project_id, 'fixed_in_version' ) : 0;
+		$t_target_version_id = isset( $t_issue['target_version'] ) ? mci_get_version_id( $t_issue['target_version'], $t_project_id, 'target_version' ) : 0;
 
 		$this->issue = new BugData;
 		$this->issue->profile_id = 0;
@@ -297,11 +290,7 @@ function validate() {
 			}
 		}
 
-		### NOTE: wasn't in mci_issue_add()
-		helper_call_custom_function( 'issue_create_validate', array( $this->issue ) );
-
-		$t_cf_result = mci_project_custom_fields_validate( $t_project_id, $t_issue['custom_fields'] );
-		ApiObjectFactory::throwIfFault( $t_cf_result );
+		mci_project_custom_fields_validate( $t_project_id, $t_issue['custom_fields'] );
 
 		if( isset( $t_issue['attachments'] ) && !empty( $t_issue['attachments'] ) ) {
 			if( !file_allow_bug_upload( $t_issue_id ) ) {
@@ -313,6 +302,9 @@ function validate() {
 			$this->files = $t_issue['attachments'];
 		}
 
+		### NOTE: wasn't in mci_issue_add()
+		helper_call_custom_function( 'issue_create_validate', array( $this->issue ) );
+
 		### NOTE: wasn't in mci_issue_add()
 		# Allow plugins to pre-process bug data
 		$this->issue = event_signal( 'EVENT_REPORT_BUG_DATA', $this->issue );