We aren’t sure what’s wrong on your end. We tested your current key: zpub6nS59yEwTZKbuxX5bVfRzLC6Z7htPapcUTn3JWjQouWwyz4R17Za7c3ymS7UGCSds1jNVWCr8Diuiq4uF8E98s7Nyg2oWYvTCWwSVLQo8cf on a fresh account and received: ltc1q0jgm0vny4whlxrztwdpraf3thut9v8rcrsgfuh. Try to create a brand new account, enter that public key for Litecoin, and create a new invoice. Your payment screen should generate the correct address.