diff --git a/src/resources/customers/costs.ts b/src/resources/customers/costs.ts
index 0b81cfd0..aa6373f7 100644
--- a/src/resources/customers/costs.ts
+++ b/src/resources/customers/costs.ts
@@ -144,13 +144,13 @@ export class Costs extends APIResource {
    * `grouping_value` and `secondary_grouping_value` available.
    */
   list(
-    customerId: string | null,
+    customerId: string,
     query?: CostListParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<CostListResponse>;
-  list(customerId: string | null, options?: Core.RequestOptions): Core.APIPromise<CostListResponse>;
+  list(customerId: string, options?: Core.RequestOptions): Core.APIPromise<CostListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     query: CostListParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.APIPromise<CostListResponse> {
@@ -297,16 +297,16 @@ export class Costs extends APIResource {
    * `grouping_value` and `secondary_grouping_value` available.
    */
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query?: CostListByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<CostListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     options?: Core.RequestOptions,
   ): Core.APIPromise<CostListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query: CostListByExternalIDParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.APIPromise<CostListByExternalIDResponse> {
diff --git a/src/resources/customers/credits/credits.ts b/src/resources/customers/credits/credits.ts
index c2fcf2ee..bbe55a06 100644
--- a/src/resources/customers/credits/credits.ts
+++ b/src/resources/customers/credits/credits.ts
@@ -16,16 +16,16 @@ export class Credits extends APIResource {
    * Returns a paginated list of unexpired, non-zero credit blocks for a customer.
    */
   list(
-    customerId: string | null,
+    customerId: string,
     query?: CreditListParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListResponsesPage, CreditListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListResponsesPage, CreditListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     query: CreditListParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListResponsesPage, CreditListResponse> {
@@ -42,16 +42,16 @@ export class Credits extends APIResource {
    * Returns a paginated list of unexpired, non-zero credit blocks for a customer.
    */
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query?: CreditListByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListByExternalIDResponsesPage, CreditListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListByExternalIDResponsesPage, CreditListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query: CreditListByExternalIDParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<CreditListByExternalIDResponsesPage, CreditListByExternalIDResponse> {
diff --git a/src/resources/customers/credits/ledger.ts b/src/resources/customers/credits/ledger.ts
index 2e70a0eb..ae38cf25 100644
--- a/src/resources/customers/credits/ledger.ts
+++ b/src/resources/customers/credits/ledger.ts
@@ -91,16 +91,16 @@ export class Ledger extends APIResource {
    * entry will be added to the ledger to indicate the adjustment of credits.
    */
   list(
-    customerId: string | null,
+    customerId: string,
     query?: LedgerListParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListResponsesPage, LedgerListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListResponsesPage, LedgerListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     query: LedgerListParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListResponsesPage, LedgerListResponse> {
@@ -225,7 +225,7 @@ export class Ledger extends APIResource {
    * return to the customer, up to the block's initial balance.
    */
   createEntry(
-    customerId: string | null,
+    customerId: string,
     body: LedgerCreateEntryParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<LedgerCreateEntryResponse> {
@@ -344,7 +344,7 @@ export class Ledger extends APIResource {
    * return to the customer, up to the block's initial balance.
    */
   createEntryByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     body: LedgerCreateEntryByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<LedgerCreateEntryByExternalIDResponse> {
@@ -438,16 +438,16 @@ export class Ledger extends APIResource {
    * entry will be added to the ledger to indicate the adjustment of credits.
    */
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query?: LedgerListByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListByExternalIDResponsesPage, LedgerListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListByExternalIDResponsesPage, LedgerListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query: LedgerListByExternalIDParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<LedgerListByExternalIDResponsesPage, LedgerListByExternalIDResponse> {
diff --git a/src/resources/customers/credits/top-ups.ts b/src/resources/customers/credits/top-ups.ts
index 45784998..d201745d 100644
--- a/src/resources/customers/credits/top-ups.ts
+++ b/src/resources/customers/credits/top-ups.ts
@@ -17,7 +17,7 @@ export class TopUps extends APIResource {
    * top-up will be replaced.
    */
   create(
-    customerId: string | null,
+    customerId: string,
     body: TopUpCreateParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<TopUpCreateResponse> {
@@ -28,16 +28,16 @@ export class TopUps extends APIResource {
    * List top-ups
    */
   list(
-    customerId: string | null,
+    customerId: string,
     query?: TopUpListParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListResponsesPage, TopUpListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListResponsesPage, TopUpListResponse>;
   list(
-    customerId: string | null,
+    customerId: string,
     query: TopUpListParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListResponsesPage, TopUpListResponse> {
@@ -53,7 +53,7 @@ export class TopUps extends APIResource {
   /**
    * Delete top-up
    */
-  delete(customerId: string | null, topUpId: string, options?: Core.RequestOptions): Core.APIPromise<void> {
+  delete(customerId: string, topUpId: string, options?: Core.RequestOptions): Core.APIPromise<void> {
     return this._client.delete(`/customers/${customerId}/credits/top_ups/${topUpId}`, {
       ...options,
       headers: { Accept: '*/*', ...options?.headers },
@@ -70,7 +70,7 @@ export class TopUps extends APIResource {
    * top-up will be replaced.
    */
   createByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     body: TopUpCreateByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<TopUpCreateByExternalIDResponse> {
@@ -84,7 +84,7 @@ export class TopUps extends APIResource {
    * Delete top-up by external ID
    */
   deleteByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     topUpId: string,
     options?: Core.RequestOptions,
   ): Core.APIPromise<void> {
@@ -98,16 +98,16 @@ export class TopUps extends APIResource {
    * List top-ups by external ID
    */
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query?: TopUpListByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListByExternalIDResponsesPage, TopUpListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListByExternalIDResponsesPage, TopUpListByExternalIDResponse>;
   listByExternalId(
-    externalCustomerId: string | null,
+    externalCustomerId: string,
     query: TopUpListByExternalIDParams | Core.RequestOptions = {},
     options?: Core.RequestOptions,
   ): Core.PagePromise<TopUpListByExternalIDResponsesPage, TopUpListByExternalIDResponse> {
diff --git a/src/resources/customers/usage.ts b/src/resources/customers/usage.ts
index 8e6c3aff..700354b6 100644
--- a/src/resources/customers/usage.ts
+++ b/src/resources/customers/usage.ts
@@ -104,7 +104,7 @@ export class Usage extends APIResource {
    * using multiple calls with small adjacent (e.g. every hour) timeframes.
    */
   update(
-    id: string | null,
+    id: string,
     params: UsageUpdateParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<UsageUpdateResponse> {
@@ -215,7 +215,7 @@ export class Usage extends APIResource {
    * using multiple calls with small adjacent (e.g. every hour) timeframes.
    */
   updateByExternalId(
-    id: string | null,
+    id: string,
     params: UsageUpdateByExternalIDParams,
     options?: Core.RequestOptions,
   ): Core.APIPromise<UsageUpdateByExternalIDResponse> {