Please note: adding additional payment methods is only available on the Advanced and Premium plans
Make sure that you have already added a delivery method called Cash on delivery.
Go to Settings > Payments > Click on + Payment method.
Add the custom name: Cash on delivery.
Also change the message template. This message is displayed when the order is placed.
Remove the info, for example, about your bank account number and add a few sentences related to the way the customer can pay when the order is delivered.
Finally, connect this type of payment with the appropriate delivery method – i.e. cash on delivery.