ePID not found EBAY_MOTORS

I seem to be unable to list anything with an ePID in the EBAY_MOTORS marketplace. Here's the "product" section of my body when my code creates the inventory item:

NOTE: I have taken the ePID and categoryId from the "US_Parts_Catalog20220204" file downloaded from eBay.

body['product'] = { 'title': @json_obj[:title],
                            'epid': "253785920",
                            'description': @json_obj[:description],
                            'long_description': @json_obj[:long_description],
                            'aspects': { 'Feature1' => ['feature 1.0', 'feature 1.1'], 'Feature2' => ['feature 2'],
                                'Brand' => ["test"], 'mpn' => ["test"]
                            }
        }

I have the marketplaceId and categoryIds set when I go to create the listing itself:

body = {
          'sku' => @json_obj[:sku],
          'marketplaceId' => 'EBAY_MOTORS',
          'format' => 'FIXED_PRICE',
          'availableQuantity' => 1,
          'categoryId' => "33601",
          'listingDescription' => 'xxxxxxxxx',
          'merchantLocationKey'=> 'xxxxxxxxx',
          'listingPolicies' => { 
                ......

With the following error:

{"listingId":"xxxxxxxx","warnings":[{"errorId":25402,"domain":"API_INVENTORY","subdomain":"Selling","category":"REQUEST","message":"System warning. The product with ePID value 253785920 was not found in the eBay catalog. It has been dropped from the listing.","parameters":[{"name":"0","value":"253785920"}]}]}

The ePID and category pairing is valid as per their document. Other pairings give the same error. Am I missing something fundamental?