Will Mobile Passport plus work 100% of the time?

No. Travelers may still receive an error message while using the Mobile Passport App. The app was designed to reduce the associated administrative and operating functions carried out by CBP, increase the quality of inspections, streamline the traveler’s inspection process, and shorten overall entry wait time (as compared to traditional primary processing). However, due to various reasons, users may still receive an error message indicating an unsuccessful submission.