When attempting to change extension numbers in Account Manager, you get an error message saying the extension is already in use, even though the desired number appears available.
This error is easily resolved by a consultation with our Tech Support team. Please create a case with 8x8 Technical Support.
This can happen if you have ever closed a line of service without changing the extension number associated with it. Though rare, it can trick the system into the thinking the extension is still in use.