Can a business deduct reimbursed expenses only once reimbursed?

[Kevin Grove]

At what point can a business deduct a reimbursed expense: On the date incurred or on the date reimbursed?

Example

I use my personal credit card to pay for some business expenses at the end of 2019. The business reimburses me in 2020.

Should the business deduct those expenses in 2019, when they were originally incurred, or in 2020, when the business reimburses me?

Would it make any difference if my business uses the cash or accrual basis?