When my customer (or I) try to pay a quickbooks invoice via ACH, we get the error message "Your payment method was declined. Please use another method or try again."

I know how important it is for a business to process invoice payments smoothly. I have some recommendations that you can do to resolve the payment declined error message, Diana.

When processing payments, declines are often caused by your financial institution. To verify this, I recommend contacting your bank to identify any issues preventing you from paying the invoice via ACH.

If you have done that and verified that there's no issue on their end. You can use another payment method to check if you can pay the invoice.

However, if you have already used all of those recommendations and the issue persists, I highly suggest contacting our Payments support team. They have specific tools to pull up your account and further investigate the root cause of the declined payment message. Doing this, they can provide additional steps to help you fix it. 

Moreover, I've attached this helpful resource that you can use as a guide in resolving ACH payment rejection codes and ways to handle them: Fix rejected ACH payments or fees in QuickBooks Payments.

I'll be here in the Community to assist if you have additional concerns when processing invoice payments. Don't hesitate to leave a reply below. Have a good one.