SMS Failure - Cause value: Protocol error, unspecified

Dear Experts.

During SMS Sending we received above cause Value that lead to failed the SMS.

Coverage and Quality satisfactory on that point.

What is reason of this Cause Value?

image

Is call happening?

Yes, call happens, but SMS fail.

Core network → You should trace with them.

But call smoothly connect, after delay sms sent.

Is your network is VoLTE capable or are these SMS over SGs/smsc?