We are currently experiencing performance issues on the Messaging API endpoint.
Some API calls may return
"SMSMessageData": { "Message": "InternalServerError", "Recipients": [] }
Our infrastructure team is looking into this, we will give an update as the investigation and resolution progress.
[RESOLVED] There was an external service that the API fetches some data from that had an outage hence causing the timeouts whe the API calls were getting processed.