get https://stage-api.findity.com/api/v1/expense/me/organizations//categories//representationtypes
For receipts where the category has the type RepresentationExpenseCategory that category can use one or more representation types. The list of valid types is returned by this endpoint. However if you choose to use the fields endpoint you don't have to bother about this, just use the url property form the field to get the correct list of representation types