How can I accept payments from overseas via ACH with little to no fees (only flat fees if any)? Specifically from UK/South Africa

It seems that you have created two separate thread for the same issue. I have already responded to your other thread. You can check the thread here: https://www.jotform.com/answers/861101. We will attend to your concerns on the other thread.

Do let us know if you need further assistance.
Regards.