Sinking Funds in Actual Budget, Confused

I can't figure out how to track sinking funds accurately in Actual Budget.

How a have been spending:

Each month I budget $150 for Car Insurance and put it into a savings account. The $150 is my "budget." At the end of 6 months I have $900 and pay our Car Insurance with a credit card, then transfer the $900 from the savings account to the checking account and pay the credit card.

How are you tracking the $900 spend on the credit card? I have my credit cards in Actual Budget as accounts, but since I'm paying out of the sinking fund there's no category on the budget to put it in. I can make the accounts accurate, but then Actual Budget will complain about uncategorized transactions.

I budgeted the amount each month, so when I pay it, I don't have any category to put it under.