how about the username? You mentioned the error message is translated. Is it possible you are using non-latin characters in the username? We can check the logs to see what is causing the authentication error, they will show whether it’s a wrong username issue or something else.
You should enable logs on the Linux server following the instructions here, https://kb.nomachine.com/DT07S00243, and then on the Mac client, the instructions are in the 4th step of that document. The client logs should be retrieved when the player showing the authentication error is open, so after reproducing the problem, do not close the player. Send everything to forum[at]nomachine[dot]com. Please use the title of this topic as the subject of your email. Thanks!