This iPhone doesn’t have service ( iPhone 7)

"Find out what to do if you see "No service" or "Searching" in the status bar. You might not be able to make or receive calls on your iPhone if you have certain settings turned on, if your software isn't up to date, or if there's a problem with your network." Read this support article if you can‘t make or receive calls on your iPhone --> If you can't make or receive calls on your iPhone - Apple Support

Also read this slightly different list of possible reasons and things to try if you see No Service, Searching, or SOS on your iPhone or iPad --> If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

iPhone 7 Plus, iOS 15

Troubleshooting:

1.

Please check -> iPhone 7 Repair Program for "No Service" Issues

iPhone 7 Repair Program for "No Service" Issues - Apple Support

2. 

If it doesn't help, remove and reinsert the SIM card.

If it doesn't help visit your carrier, maybe the SIM card is damaged, ask for a replaced (new) card. Normally it is free.

Ask also to check if the SIM tray is bent, as even a tiny misalignment can cause the SIM card to not fully connect with the internal contacts in your iPhone.

3.

See these Apple articles below:

If you see No Service, Searching, or SOS on your iPhone or iPad

If you see No Service, Searching, or SOS on your iPhone or iPad - Apple Support

Manually update your carrier settings on your iPhone or iPad

Manually update your carrier settings on your iPhone or iPad - Apple Support

Update your network provider settings manually on your iPhone or iPad

Update your network provider settings manually on your iPhone or iPad – Apple Support (UK)

If you see a Cellular, Ultra Wideband, or Apple Pay Issue message after an iOS update or restart

If you see a Cellular, Ultra Wideband, or Apple Pay Issue message after an iOS update or restart - Apple Support

4. 

iPhone 7 is > 6 years old, which also affects the battery life. The hardware remains old, so does the battery.

If it is still possible, have the battery replaced.

The battery can be replaced by Apple or an Apple Authorized Service Provider.

See this Apple article: iPhone Battery Repair & Replacement - Apple Support

If you are going to replace the battery, see -> Get your iPhone, iPad, or iPod touch ready for service

Get your iPhone, iPad, or iPod touch ready for service - Apple Support

The price is approx $ 69.

If you want to know exactly, call Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

or 

call 1-800-MY-APPLE

With an iPhone 7 look at this document:

iPhone 7 Repair Program for "No Service" Issues - Certain US and Asian models

iPhone 7 Repair Program for "No Service" Issues - Apple Support

BUT:

"The program covers affected iPhone 7 devices for 4 years after the first retail sale of the unit." The iPhone 7 sold September, 2016 - September 2019 so eligibility will depend upon when exactly you bought your iPhone 7.

Leennkyo ~ Does your iPhone 7 Plus still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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