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SMS problem - 337 error

New Contributor



I'm trying to setup Sinch in an app I'm making for a US-based client. The client has given me the api key, the service plan id and a from number. Trying to send a test message with a full delivery report and a callback url returns a report of a failed sms with the error code 337 which is as I can see on the error list "Invalid optional parameter".

Now, when I try the same message with my own test credentials it works, I receive the SMS and the delivery report says "delivered".


So, any idea what the problem is here?


Community Manager
Community Manager

Thanks for your question. I have escalated this to our SMS team who will look into this for you.


Kind regards,

Shahzad Ismail
Head of Knowledge Management and Community Engagement, Sinch

Community Manager
Community Manager

Note: This user was contacted via direct message and their issue was resolved. A summary of that resolution is included below for future reference.


There were a couple of contributing factors that led to the issues experienced by this user, but the most relevant issue was that the user's US-based client needed to set up a 10DLC campaign.


10DLC campaigns are required to send SMS messages in the US region. Readers can visit our knowledgebase for 10DLC, which contains articles that will be able to provide more general and contextual information on 10DLC.

Sam Williams, Sinch Documentation Engineer