Returned when a cpk_test_* key is used against an environment that only accepts live keys (or vice-versa). 
{ "error": { "code": "partner_mode_mismatch", "message": "test-mode keys are not accepted on this environment" } }
Fix — use your cpk_live_* key against production (partners.crewpass.co.uk) and your cpk_test_* key against the sandbox.