The biggest voip provider in our country uses Username and authentication on the trunk with the symbols. Like XXX_X@XXXX . And in Yeastar devices we can't create SIP TRUNK with those symbols.
This structure of username is made by biggest VoIP provider in our country. There's no way it can be changed.
Moreover Asterisk, Avaya, Alcatel and any other PBX'es have no issues with symbol "@" in username. Please let me know if you can solve this issue or should I notify all our customers and providers, that Yeastar's PBX'es are not suitable for our country.