If the message is “PIN unlock key (PUK)” or "Enter PUK Your SIM Card, SIM cannot be accessed" or on an iPhone's status bar showing "Locked SIM"
You can try if the default sim pin: 1234 works
If you have an eSIM: a quick way is to buy a new eSIM using the app. Login PM app on the phone. (If you have problem with receiving 2FA code, click "Didn't Receive code" or "Resend code" and choose either "Send email" or "Send Voice Message") Once logged in, Click Account from the bottom, then click Purchase SIM Card and select eSIM and follow the prompt to complete and purchase and install eSIM on your device