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Failed send SMS to some numbers.

New Contributor
When I send SMS via API to one number it delivers fine. When same code do it for another number it is not delivered. Saying the "337 - Invalid optional parameter"

Both numbers are "verified" so they should be able to receive SMS from Sinch

Code that I use to send a SMS

Please advise what could be an issue. What optional parameter I should path to API.

Community Manager
Community Manager

Hello, thank you for reaching out!


We reached out to the SMS team for information, and they indicated that this type of error code can sometimes require more investigation in order to resolve. The team recommends reaching out to the Sinch Support team for assistance.


To contact the Sinch Support team, please follow the guidelines in the Sinch Customer Support Process.

Please let us know if you have any other questions.

Thank you!

Sam Williams, Sinch Documentation Engineer