I haven't seen any clear instructions to do this in internet, so I hope it comes handy to someone.
- Go to https://developer.apple.com/account/resources/identifiers/list/merchant.
- Select identifiers.
- At the side of the magnifier icon (to filter), click on
Merchant IDs. - Now click on the
+icon to add a new record. Now Make sure thatMerchant IDsis selected and click Continue. - In
Descriptiontype a representative name for this Merchant ID record (I useName of the Bussiness + ENV, likeAwesome cakes test) andIdentifieruse the reverse-domain name style here (it's up to you it's just an id, I usemerchant.com.awesomecakes.myapp.test). - Click on Continue and click Register.