Mor authorize: Too low balance for more simultaneus calls!!!

The other reason can be that your user is PREPAID and he has not enough balance to cover more simultaneous calls.

MOR uses algorithm to reserve balance when call is made to be safe if user is prepaid.

That way when second, third, etc calls are made - MOR checks free - not reserved balance and decides should it allow to dial or not.

To lower security level and allow users with low balance to dial out several times, go to /etc/asterisk/mor.conf and change to:

min_frozen = 1

That way you are taking risk that you will take loss if user talks for more then frozen_time (default 90s). E.g. if user make a call, his balance is frozen for 90s with the rate to current destination. If user talks more - you can take loss.