The first thing to check when you want to assign a product to a Reservation Type is that you have the product created with the right price. This check can be done from the Settings/Services menu.
If the product is not available, it must be created from the Settings/Services menu. You can see step by step how a product is created in the article found below.
Once the product is created, it is now possible to go ahead and configure the reservation type following the steps below:
Go to the menu Reservations/Reservation Types.
Search and find the Reservation Type you would like to add the product into. If you need to create a new Reservation Type. The article for this can be found here
Click on Edit.
In the product field, click on the drop-down and select the product you want to assign from the list.
5. To finish, click on Save.