...
Since at this point it's very possible we are experiencing a configuration problem on the server side, you have to check deeply the User's account configuration: is the User accounted on the PBX? Is his/hers account registered? Is there any virtual number duplication? Is the Account configuration compatible with the client one (check the obfuscation for example).If all this checks go fineactivities on the server in order to discover some conflict, such as a virtual number duplication, if it does then resolve the conflict and close the incident. If it doesn't, then we need to perform some tests on the PrivateServer status: Network and PSAM 3.3 Check Server Services.
If all of the above are fine, the final possibility of a bug in the client become feasablebecome feasible, thus we check the client logs and then we escalate.