diff --git a/src/messages/StopTransaction.cpp b/src/messages/StopTransaction.cpp
index 5b51e810..d25ffd50 100644
--- a/src/messages/StopTransaction.cpp
+++ b/src/messages/StopTransaction.cpp
@@ -56,7 +56,10 @@ bool StopTransactionReqConverter::fromJson(const rapidjson::Value& json,
     extract(json, "meterStop", data.meterStop);
     bool ret = extract(json, "timestamp", data.timestamp, error_message);
     extract(json, "transactionId", data.transactionId);
-    data.reason = ReasonHelper.fromString(json["reason"].GetString());
+    if (json.HasMember("reason"))
+    {
+        data.reason = ReasonHelper.fromString(json["reason"].GetString());
+    }
     if (json.HasMember("transactionData"))
     {
         const rapidjson::Value& transactionData = json["transactionData"];
@@ -83,7 +86,10 @@ bool StopTransactionReqConverter::toJson(const StopTransactionReq& data, rapidjs
     fill(json, "meterStop", data.meterStop);
     fill(json, "timestamp", data.timestamp);
     fill(json, "transactionId", data.transactionId);
-    fill(json, "reason", ReasonHelper.toString(data.reason));
+    if (data.reason.isSet())
+    {
+        fill(json, "reason", ReasonHelper.toString(data.reason));
+    }
     if (!data.transactionData.empty())
     {
         rapidjson::Value    transactionData(rapidjson::kArrayType);
diff --git a/src/messages/StopTransaction.h b/src/messages/StopTransaction.h
index cc855d02..1040098a 100644
--- a/src/messages/StopTransaction.h
+++ b/src/messages/StopTransaction.h
@@ -51,7 +51,7 @@ struct StopTransactionReq
     int transactionId;
     /** @brief Optional. This contains the reason why the transaction was stopped. MAY only
                be omitted when the Reason is "Local". */
-    ocpp::types::Reason reason;
+    ocpp::types::Optional<ocpp::types::Reason> reason;
     /** @brief Optional. This contains transaction usage details relevant for billing purposes */
     std::vector<ocpp::types::MeterValue> transactionData;
 };