Old and new software generations do not connect to each other, it seems like the issues is there, you are using new server with old client, it won't work.
1. We do not support ExpertSDR2 since the beginning of 2021.
Through 2021 we've released new versions of ExpertSDR2 only with new firmware, but without any other changes, so users could jump from ExpertSDR2 to ExpertSDR3 and back without flashing firmware.
With the release of ExpertSDR3 0.12.0 in Spring 2022, we've released an absolutely new firmware which is incompatible with ExpertSDR2, so now you'll have to flash firmware to jump back and forth between software versions.
ExpertSDR2 1.3.1 Update 11 is the last of its kind with SDR firmware v. 72.8.
Current version of ExpertSDR3 is 1.0.1 Beta with SDR firmware v. 86.8.