Service user can't read user key with keyctl: keyctl_read_alloc: Permission denied

$ sudo -u backup_agent keyctl add user LUKS_PASSWORD "your-secure-password" @u1013632990$ sudo -u backup_agent keyctl list @u1 key in keyring:1013632990: --alswrv   110   110 user: LUKS_PASSWORD$ sudo -u backup_agent keyctl read 1013632990keyctl_read_alloc: Permission denied

I'm trying to create a key for a service user that it would use from a script later from a cron job.I can't understand why the last step above results in a permission denied error. Any ideas?