I have an account that double paid an invoice on (2) separate dates. With this 2nd payment, how do I apply it since the account is at a zero balance?

Thanks for reaching the Community forum, BB444.

I'd love to assist you with this issue. However, I kindly request more details about how you applied for these payments to provide the most accurate solution,

Did you pay your vendor two separate dated bills? Have you applied the first payment to the other invoice, which caused the account to have a zero balance? Or did you mean that your customer has paid your invoice twice, and then you're trying to apply these payments to the invoice?

I'll leave material here explaining how to credit customer accounts from overpayments for future use: Create and apply credit memos or delayed credits in QuickBooks Online.

I am committed to quickly resolving your payment matter to meet your work requirements. Please provide the requested information, and I will promptly address it and offer the guidance you need.