Cannot INSERT: ERROR: array value must start with "{" or dimension information
Your column username seems to be an array type, so the literal 'mahman' is not valid input for it.
It would have to be '{mahman}':
INSERT INTO user_data.user_data (username,randomint)VALUES ('{mahman}',1);(Or make it a plain varchar column or text column instead.)
Update confirms it: character varying(50)[] is an array of character varying(50).