Audits are not billable for operations

No, this is not billable work. Audits are not projects. They are included in the MSA. Audits are done every year.

If you need to do any preparation work yourself, then that is at your cost – the theory being that you should be able to be audited at any time without having to prepare for it. Normal operations should be audit compliant at all times.

The audit is just a check of this.