During a call the dialpad may need to be used to enter responses such as IVR menu choices. However, these do not appear to be working once the call has been established.
What To Check
Please check to see if RFC2833 or the newer RFC4733 DTMF methods are supported.
Please examine any traces captured to ensure DTMF is negotiated correctly throughout the entire call.
In the Border Gateway or PBX, change the DTMF Payload to accept 101. Teams sends out a DTMF payload of 101.
If the above steps do not reveal the issue, please raise a case including any trace captures and the call URL within the call log in the portal.