Hello, thank you for reaching out!
Based on your previous post, it looks like you are trying to use the MMS functionality of the SMS API. At this time, only mobile terminated MMS messages are supported on the SMS API (that is, only sending MMS messages is supported by the SMS API at this time). Support for mobile originated MMS messages is currently under development. Please also note that:
If you are experiencing issues with receiving MMS messages using another API (for example, the MMS channel of the Conversation API or Sinch's standalone MMS APIs), or if you have any other questions to ask or context to provide, please feel free to add another reply to this post.