Here's what we've learned about some common issues with these payment processors.
When your customers pay with MasterCard or VISA, you don't get your money right away.
Instead, they're paid out weekly, accompanied by a PDF statement which you receive by email from Teller.
The transaction on your bank statement will say something like "FNR. xxxxxxx" where xxxxxxx is your 7-digit PBS/Nets/Teller merchant number.
The weekly PDF statement, called an "Advisering", contains a reference to a Ref. Nr. of the form " 000BILPxxxxx", where xxxxx is the transaction ID, which you will find next to the invoice when you click on Reporting > Invoices in your admin interface.

Sometimes a PayPal payment doesn't register in Simplero, even though it's gone through in PayPal. The way Simplero knows that the payment has gone through is that PayPal sends us what's called an IPN, short for Instant Payment Notification.
Without this, we have no way of knowing the transaction went through. So if this doesn't get to us, that's a problem.
Follow the instructions in this article to resolve the issue moving forward.

These cases are very likely due to PayPal returning the status "Pending" instead of successful at the time of the purchase. Then, later on, updating to successful.
When this happens, you can click on "Try to activate" to update the purchase status.

What happened here is QuickPays server didn't communicate with us that the payment was successful. As this is on QuickPays' side, there is nothing we can do about that.
However, what you do need to do in Simplero is register the payment manually. This is VERY important in order to keep your accounting accurate and avoid any discrepancies.
Here's what you need to do:
Log in to your QuickPay Manager
Confirm the payment went through
Once you've confirmed the payment, you'll need to register the payment in Simplero
Select Products from your Simplero Dashboard
Select the Purchases tab
Locate and select the purchaser (customer's name)
In the Charges & Payment section, click the Register payment button
The Register payment screen will open
Enter the amount received, select the date paid, and the method. Add a comment so you can identify the payment in the future. You could add something like "QuickPay Network Error" and be sure to double-check that the amount is accurate.
Once all looks correct, click the Register payment button to save
The purchase will now have a registered payment. The owing charge should match with the payment you just registered.
Payment processors often have time limits on refunds. If you are trying to refund an older purchase that is past the payment processor's refund period, it will register that they've been refunded in Simplero, but no transaction will have gone through on the processor.
If this is the case, you'll need to refund the customer their money some other way (perhaps by sending them a check).
Here are the refund periods for our common payment processors. If you are having trouble refunding with a payment processor not listed here, be sure to check with them what their refund period is:
Upsell and order bump products are not available via PayPal. - If PayPal is not showing as an available payment processor on the product order form, make sure the product does not have any available upsells.

Once a purchase has been created (either manually or through the product order form) and a payment method has been selected, PayPal will no longer show up as an available payment method. Even though it is available as a payment method in the price settings.
The reason is that PayPal cannot be set up unless a charge is due.
As soon as you add an outstanding charge, PayPal will show up as an available payment method in the manage payment page.
If you get an error saying: This PaymentIntent could not be captured because it has a status of canceled. Only a PaymentIntent with one of the following statuses may be captured: requires_capture

Note that Authorize lasts “up to seven days" - If the purchase was created before 7 days ago, Stripe is not letting us collect the money, and you may need to ask the end-user to place a new order.