The "Manual" payment processor is for any form of payment that Simplero can't handle automatically for you. That would include payment by check, by wire transfer, by cash in hand, sheep, Western Union, or whatever else you could think of.
You can add a Manual payment processor under Settings > Payment processors > Add new payment processor, and choose Manual. You can call it anything you like.
We have two by default: "Cash" and "Bank transfer". They're not enabled. If you want to offer manual payment, then you need to enable them first, but before you do, please go edit them to add the relevant instructions for how to pay, eg. your routing number and account numbers, or any other necessary information.
How It Works
On the checkout screen, if enabled, your customers can choose one of the manual payment processor, eg. "Bank transfer".
On the next screen, they'll see a notice informing them of the amount to pay, the ID number to reference with their payment, and the instructions from the payment processor they chose.
The purchase will now be listed on your dashboard, so you can remember to keep an eye out for their payment.
Once you see the payment come through, click the correct purchase on the dashboard. The purchase will say how much money we're expecting and through which channel. If the money's there, click the "Register payment" button on the purchase screen, and enter the amount they paid and any additional information. You can also change the payment processor, if they happened to pay some other way.
After you complete the dialog, assuming they paid enough, the purchase will be activated, and the normal activation sequence is run (auto-responses, access to content, invoice, login info, etc.).
Why We Don't Send an Invoice Right Away
If this was a "normal" business, you'd be sending an invoice to the company, and their accounting department would pay the invoice. We don't do that here, because online shoppers are more flaky. They might just be thinking about buying, and not be serious.
The problem with issuing a formal invoice is that, for most accounting purposes, that's considered booked revenue, even if the money isn't there yet. And in this case, it may never arrive. In which case, if you have issued an invoice, you need to issue a credit note and argue for why the money never showed. It's just an additional, unnecessary hassle.
So we don't send an invoice. If people want the stuff, they'll pay, and we'll give it to them.