How do I create a MetaMask transaction that only shows the gas fee and not the transaction amount

Question

I want to create a dapp that when you click on pay with prior notice of the amount you are paying for , when your MetaMask interface shows up it only shows the gas fee you are paying to get that payment done and not the real amount it self. Somebody has done this before but I don’t seem to know how he did it. So I seriously need an answer thanks.