Once the process shows "Done" (usually 2–5 minutes), the phone will reboot. Upon restart, inserting a non-T-Mobile SIM (e.g., AT&T or Verizon) should no longer show an "Invalid SIM" error.
Download the T-Mobile Device Unlock (Pixel) app from the Play Store. VARIO UNLOCK TOOL TMOBILE-MOBILE PHONE
Download the T-Mobile Device Unlock (Pixel) app from the Play Store, open it, and select Permanent Unlock . The Ultimate Guide to the VARIO Unlock Tool