iPhone 14 SIM Unlock

I have an iPhone 18 that reports “SIM card or network not supported” whenever I insert a non-original carrier’s SIM. The handset itself is fully functional; the lock is strictly at the network level—no passcode, no iCloud activation lock issues are involved... (Budget: $10 - $40 USD, Jobs: iOS, iPad, iPhone, Mobile App Development, Mobile Development, Mobile Repair, Objective C, Software Development, Technical Support, Telecommunications Engineering)