No TAPI lines are created via the function "Create lines" in XPhone Server under SETTINGS -> PBX -> FIXED NETWORK.
First make sure that the TAPI lines are provided by the TAPI Service Provider. You can see this e.g. by the Windows dialer help (dialer.exe).
If the TAPI lines are available at the XPhone Server and licensed, but not created by the mentioned function, the phone number format may have to be adjusted.
The line address of the TAPI line is 99123. 99 is a node or cross connection code, the number 123 is the actual extension number.
The used trunk header is (089)123456-0
Now open the properties of the created PBX node and add a parameter at "Advanced settings". Name this AdaptAddressNumbers and store the following value: 99||089123456
Save this setting until you are back in the overview of the PBX nodes and now create the lines again.