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It would have been a good option if rate-limit configure option would have been provided to the users to configure on their API. Need an enhancement if possible, that will reduce complexity and empower user to put the rate-limit as per their use case without involving Dev support team in every case.

Is it important that everyone receive the SMS from the same number? If so, why is that the case here?

This limit is not configurable at the moment but it's good to get more information on use cases.

Yes, that could work but it will be coming from two numbers instead of just one. 

To send the SMS to all 80+ users at the same time without delay, send the message from 2 extensions where each extension will have a separate rate limit. Break your users into groups of 50 or less and send from separate extensions where each extension has a SMS capable phone number. The numbers can be either direct numbers or digital lines.

Does that help resolve this situation?

I have a need to send identical SMS to 80+ users. How do i achieve this without hitting the 50 Rate limit