This applies to both Stripe and Square online payments.
Step 1. Create the invoice -> click the SMS or Email option -> OK -> This will send across the invoice link for your client to pay online.
When the client clicks on the link it opens a window to the payment gateway for the patient to enter their card details and pay (as below image). These details and the payment is handled by your merchant and not ever saved in SimpleClinic.
You will receive a notification that a payment has been received and the invoice will be automatically marked as paid with the ONLINE method.
If you have multiple payment gateways connected, the default for use is Square first -> Stripe. You cannot use more than one for online payments.