For ACH / checking account payments I have set up Authorize.net gateway.

I usually set up my Authorize.net checking transactions as PPD (if that makes any difference).

I also have set up Stripe but only for credit & debit cards.

All of my customers pay recurring monthly subscription fee, usually billed on the 1st of the month.

Some of them also incur extra charges from time to time that are billed separately from the subscription fee.

The extra charges shouldn't be combined with the monthly subscription charges for various purposes.

Authorize.net takes about 14 days to clear payment from bank checking account.

During that 14 day period, if I create a new invoice, the option to use Authorize.net is grayed-out.

In other words, I cannot initiate a new Authorize.net transaction while the previous one is still being processed.

Does anybody know how to "fix" that, or a work-around?

Or is there some hardwired prohibition against multiple ACH payments being processed concurrently?

Again, using just 1 gateway to process both payments, in roughly the same time period.