PostgreSQL permissions explained
The error says permission denied for schema public (emphasis mine)
You need to give readonlyuser rights on schema public:
GRANT USAGE ON SCHEMA public TO readonlyuser;The contents of the ACL is explained on this page. The most relevant part quoted here:
rolename=xxxx -- privileges granted to a role =xxxx -- privileges granted to PUBLIC
r -- SELECT ("read") w -- UPDATE ("write") a -- INSERT ("append") d -- DELETE D -- TRUNCATE x -- REFERENCES t -- TRIGGER X -- EXECUTE U -- USAGE C -- CREATE c -- CONNECT T -- TEMPORARY arwdDxt -- ALL PRIVILEGES (for tables, varies for other objects) * -- grant option for preceding privilege /yyyy -- role that granted this privilege
The + are part of the way psql formats the result, they are not part of the value.