Azure Database for PostgreSQL flexible server - Cannot grant permission to pg_cron schedule to roles

Azure Database for PostgreSQL flexible server -
I'm trying to set up pg_cron so the relevant role can schedule jobs.

I'm logged in with an account with azure_pg_admin role.

I can use cron under this role, e.g. setting up the housekeeping cron works fine:

SELECT cron.schedule('0 0 * * *', $$DELETE   
    FROM cron.job_run_details   
    WHERE end_time < now() - interval '7 days'$$);  

However I would like to set up a cron job from another role.

I try granting execute on the cron.schedule(text,text) function

GRANT USAGE ON SCHEMA cron TO my_role;  
GRANT EXECUTE ON FUNCTION cron.schedule(text, text) TO my_role;  

and that doesn't error but outputs:

no privileges were granted for "cron"  
no privileges were granted for "schedule"  

And I can't schedule jobs under that role.

SELECT cron.schedule('My job', '0 16 * * *', 'call myschema.myfn();');  

errors with

SQL Error [42501]: ERROR: permission denied for schema cron  

Position: 8

Are there any limits or restrictions to doing this in Azure?