Billing Price not greater than GR price, how to setup this request. please advise

Scenario,

Company process is 3pl . First internal company send PO to main company. That main comapny(MC) create SO and its convert to PR and PO. Then PO send to external supplier. Supplier directly send the goods to internal company and this internal company doing GR creation.

After that main company doing GR that compare with internal company GR. Then MC posted invoice and complete the process. Meanwhile this MC send billing to the internal company.

My actual query will be  , sometimes billing price is greater than internal company GR price. So the MC wants to control this billing process.

Please share the idea how to block when this condition happend?

Thanks

Abi.