Issues with my iPhone's signal

Try this If you can't activate your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

Your iPhone might be locked to a different carrier. Is there a way you can get a SIM from another carrier and test it with the phone?

Faytsa Said:

"Problem: I don’t have signal in my phone two days now, the sim it’s not the proble because I try it in another phone"

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Activating an iPhone:

Getting Around this Error:

1. Go Here: If you can't Activate your iPhone - Apple Support
2. As it Reads: If your iPhone can't be activated or an alert says the activation server is unavailable or the SIM card is unsupported, learn what to do.

Is your iPhone showing any carrier signal? If not, it might be that your phone is locked to a different carrier.