How to bind sip to a handset if there are letters in the domain?

Question

SIP

Bottom line - my cloud telephony domain contains letters.
ac3123.something.something

If I try to put this case into the Grandstream DP720 handset, I see in the network settings that the letters are "cut off", only the digital identifier remains.
In this case, the connection to the network, respectively, does not occur.
Who faced such a problem, how did you solve it?

Answer 1

Screenshot possible?