The setup.sql for postgres in 3.x

raddb/mods-config/sql/main/postgresql/setup.sql

does not grant sufficient permissions to update tables. I'm not a
postgres expert but apparently when you use a SERIAL or BIGSERIAL type
to create a unique key postgres does that by creating something called a
sequence object. After creating the schema you'll see things like this:

> psql:schema.sql:180: NOTICE:  CREATE TABLE will create implicit sequence "radpostauth_id_seq" for serial column "radpostauth.id"

Those sequence object need permission grants on them in addition to the
table grants. Currently postgresql/setup.sql does not establish these
sequence grants, as a result you'll see errors like this:

> rlm_sql (sql): Executing query: 'INSERT INTO radpostauth (username, pass, reply, authdate) VALUES('paptestuser', 'mypassword', 'Access-Accept', NOW())'
> rlm_sql_postgresql: Status: PGRES_FATAL_ERROR
> rlm_sql_postgresql: Error permission denied for sequence radpostauth_id_seq
> rlm_sql_postgresql: Postgresql Fatal Error: [42501: INSUFFICIENT PRIVILEGE] Occurred!!
> rlm_sql (sql): Database query error: ERROR:  permission denied for sequence radpostauth_id_seq 

The solution is to add these grants to postgresql/setup.sql

GRANT SELECT, USAGE on radacct_radacctid_seq TO radius;
GRANT SELECT, USAGE on radpostauth_id_seq TO radius;