If you have a zaptel card and the call is coming from PSTN to IVR and IVR is not accepting selection of digits while the IVR greeting is played, you should check that:

1. 'Relax DTMF' is set to 'Yes'. Navigate to 'Settings: Servers: SIP: Relax DTMF' and set it to 'Yes'. Save and give it a try again.
2. Check your RX gain value. Navigate to 'Trunks' edit your trunk and set 'RX gain' value to '0'.

When increasing the RX gain value, the DTMF amplitude is being increased to a value that can exceed the maximum receive level of the card, which is causing the issue in this case.