Some extension numbers cannot be assigned (77, 81...)

[Bruno PELZER - CELEM]

For one of our customers we use extensions with only 2 digits.
It works fine but we cannot assign extension number 77 and 81. When we try, we get this error :
given dn number cannot be used
It seems that those extensions are used internally... Can someone help me to properly solve this issue ?

 

[YiannisH_3CX]

Hello @Bruno PELZER - CELEM

Please note that those extensions are system extension so you cannot assign them to normal extensions are they are used by the system. The system needs these extensions to operate normally. You can see a full list of system extensions if you navigate to Dashboard / System Extensions.