When using the standalone MMS API, MMS messages cannot be submitted through an SMS Service Plan ID. The standalone MMS API does not use Service Plan ID; it uses a separate MMS API key.
Service Plan IDs are used to authenticate when using the Sinch REST SMS API. The MMS functionality of the Sinch REST SMS API is scheduled for deprecation. If you would like to gain access to MMS functionality through other products, we encourage you to explore the options listed on the Sinch MMS Overview page.
Visit the Sinch MMS product page to learn more about our MMS product.
