You've come to the right place, JulieL.
Good news! Your customers can pay via ACH using foreign bank accounts.
To make this work, your customers in Mexico will need to contact their financial institution. They will be able to provide options for using international cards with U.S. based businesses.
For additional insight on how to make this work, I highly recommend following this article: Cannot take an international credit card due to an invalid zip code
I hope this response finds you with a smile today. Let me know if there's anything else I can do for you, I always have your back. Thanks for reaching out, wishing you and your business the best.