Opportunity: Default Record Type Missing Values

I’m creating a field mapping for Salesforce Opportunities to map to a custom post type. It shows the “Allowed Record Types:” and below that there is a drop-down field called “Default Record Type: – Select Record Type -“. There are no entries in that drop-down and when I try to save the fieldmap it gives an error that says “Please select an item in the list”. Problem is, there are no items in that list to select from.

Because of this, there is no way to create the fieldmap.