Using PayPal Payflow Card on File feature for future recharging with their API
Solution 1:
You are describing reference transactions, so according to the Payflow documentation there is no need to specify CARDONFILE. It is handled for you.
To use reference transactions, save the PNREF of an initial sale transaction, delayed capture, or zero dollar authorization -- and reference it in the future for a new sale (TRXTYPE=S) with ORIGID instead of ACCT
Note that to use reference transactions they must be enabled in the settings of your Payflow Manager, and you must wait up to 1 hour after making changes to those settings.