Invoice Expense Dates - Use billed date or paid date?

[Jason Riddle]

I'm trying to understand what date to use for categorizing expenses, I have the following example.

Say someone sent me an invoice for work done on December 30th, 2022. I'm not able the pay that invoice until Jan 1st, 2023. Which date should be used for that expense? When it was billed or when it was paid?