The flood zone on the insurance policy must match the flood zone on the flood determination. The only completely acceptable difference is when the preperty has been grandfathered. Grandfathering is granted by the insurance agency. It is not something you apply for.
You need to work with the flood insurance agent and your determination company to resolve the differences. If you are unable to resolve the matter, it must be submitted to FEMA for resolution, and that will cost your customer a fee. You cannot fund the loan until a flood insurance policy in an adequate amount is in place.