Hi Mike! Thank you for visiting us here in Community. Your iPhone XS Max is currently locked? Or are you referring to it locking up when traveling to China? Also, is it currently activated with Sprint?
Okay, just letting you know, that I can verify your phone by you sending me your IMEI number in a Private Message. However, inserting a Sprint SIM card in the Sprint phone is part of the required processed to unlock a phone, IF the phone is eligible to be unlocked.