CustomHTML field value not passign for some users


I am encountering an issue with the Send Email Campaign API. Some users are unable to send the custom HTML field data successfully, while all other fields in the API call are accepted and the email campaign is created. The response indicates that the custom HTML field value is null, despite the API call returning a status of 201 (created). I have tried sending the same requestBody payload in another account and its working. I have been unable to identify any patterns or factors causing this issue. Any insights or assistance would be appreciated.

Thank you, Umar