Second-hand iPhone 7 says "No service", other times it says "Searching"

Hi!

I just bought a second-hand iPhone 7, modelA1778.

Sometimes, it says "no service", other times it says " Searching". I went on the internet and I saw that every phone that had such a problem used to have other problems, like detecting the IMEI, the ICCID and the modem firmware. They were also not capable of activating themselves when you tried a restore.

However, I do not have those problems. I restored it, I was able to activate it, and when the phone displays me all those infos.

Do you have any idea of what is the problem? What causes it? How to solve it? Can you make an estimation of the price for a repair?

Thank you very much!

Giacomo

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