Add a method to the Payment Gateways list on Shop › Settings › Payment Gateways to offer it.
Monthly Credit
Monthly Credit is a credit line you give your customers. The order is placed unpaid and you collect the money yourself later. Nothing in the panel sends a reminder or a statement for it, so keep your own record of what is owed.
Request Payment on an order
The Request Payment button appears on the order page for placed orders whose method is GCash (or UPI where the platform has enabled it), until you accept them. Above it the page shows the Payment link: for the order and the reminder "Make sure you have received payment before confirming."
Without WhatsApp sends the customer a push notification with the payment link and answers "Payment Request Send".
With WhatsApp does the same, then opens WhatsApp with a message to the customer for you to send.
Neither choice takes money or marks the order as paid. The button does not appear for Payment Via Link or Monthly Credit orders, and marketplace staff do not see it.
Recording the payment when you accept
When you accept an order that shows Request Payment, the Confirm And Accept form asks how it was paid:
Field
What to enter
Payment Mod
GCASH when a GCash number is saved, UPI where enabled, or Cash On Delivery
Payment Notes
Anything your team should know, for example the transfer reference
Choosing a method that is not on the form is refused with "Choose one of the payment methods listed."