Admin - Superuser

Online registration is an on demand payment system and only allows payment by credit card/check even if your site has ACH functionality in the billing system. We can immediately "ping" the credit card company about the CC used to determine if it's valid and has enough funds. This is not possible with ACH; it can take 5-7 business days to either fail or fund. This does not work in an on demand module such as Online Registration or Lessons.

There is a workaround, however—push the registration to billing so it gets invoiced on the 1st. See the first article below.

See Also
Use ACH to pay for registration workaround
When does the online registration charge the Credit Card?
Refunding in the online registration system