Thank you, this post helped me too!
I had tried to run Rei3 under Linux with a Postgresql 12 database, but when starting the R3 service I got the message "ERROR: function gen_random_uuid() does not exist (SQLSTATE 42 883) "
I quickly realised that my Postgresql version was too old.
After upgrading Postgresql to V 16 , the service startet, but did not accept the admin/admin crendentials.
r3 -newadmin new_user:new_password
did solved my problem