Hello lpranger!

Ideally, you should use the date when you processed the payment. Since you paid it this year, then you should use the 2021 date.

You might want to check this link to understand the difference between cash and accrual accounting methods: Cash vs. accrual accounting: What’s best for your small business?

Also, it's best to seek some help from your accountant for the proper way to enter such transactions in QuickBooks Online.

Having issues with your reconciliation? Please check this link on how to fix it: Learn the reconcile workflow in QuickBooks.

Keep on posting here if you need anything else. I'll be here!