Hi
I am getting the error while sending the test text message on mobile and I am using 3rd party mobile service for sending the message. For the integration, I am using this blog for reference
https://blogs.sap.com/2018/07/23/sap-marketing-cloud-connect-any-text-message-service-provider-to-sap-marketing-cloud-chapter-1-send-sms/#:~:text=To%20connect%20a%20custom%20text,service%20provider's%20individual%20API%20specification
Thanks & Regards
Abhinav Bhargava