String path variables in a mock

We’re just trying out postman. Someone else on the team has sent me a collection, so I can see his api documentation, and I’m trying to create a mock out of it so I can build against it.

The call is a simple GET {{ server }}/accounts/{{account_id}}. And it works fine if I use an integer as the account_id (I get the example back). When I use a hexidecimal string as the account_id I get a mockRequestNotFoundError.

How do I fix this - I’ve looked through the json for the collection and poked around the app looking for a way to specify the format of this parameter, but I can’t find anything.

How to I get my mock to accept a string path variable?