If I paid $64 when I filed an extension, do I have to pay again after I complete it? It is asking for payment again.

If you e-filed the extension request using the TurboTax Easy Extension then you should have signed onto the 2023 TurboTax online account with the same User ID and password you created for that account.  If you did there would not a requirement for you to pay for online account again except if you also created a state tax return then there would a charge of $64 for the state program.