FFP task order - invoicing breakout requirement?

Contractor is working for the military on a TO awarded pursuant to Contractor's GSA MOBIS contract. TO is FFP and provides that contractor will bill USG a fixed amount each month, say, $50,000, Contractor submitted first invoice and the COR rejected the invoice, saying that it is generally fine, but that he wants the contractor to "split out the following to capture the actual total for hours worked and the difference to come to the $50,000 amount.

Breakout

001 1‐31 March Labor Support 50,000.00

to

001 1‐31 March Labor Support $$$$$$

001 1‐31 March FFP Labor Support $$$$$$

Total 50,000.00"

After further communication, Contractor understands that the COR wants the line "001 1-31 March Labor Support" to be "actual" (i.e., the amount contractor would have invoiced had this been T&M)" and

and the line 001 1‐31 March FFP Labor Support $$$$$$ to be the "monthly lump sum invoice amount. "

Is this a legitimate request? The payment terms of neither the TO nor the MOBIS contract state what is required in an invoice and the contract terms themselves do not require such a breakout.