Can't I use LINE app on my iPhone

the link he posted to the app store for the app called LINE shows that the apps requirement is IOS17 if your phone do not support being updated further than ios16 then you have no options apart from getting a new phone or not using the app

if the service of the app developers no longer works with older app versions

dwctv wrote:

I am aware of that. All I wanted to know was whether someone had the same problem and could solve it by updating to iOS 16.7.13.

No. The iPhone 8 Plus, a phone that ran iOS 11.0 when Apple introduced the first variants in September 2017, received five major iOS updates. It can update to the latest release of iOS 16 – or will be able to do that, once Apple sorts out the issues with the January 26, 2026 release.

It cannot update to iOS 17 or later.

According to Line Help Center – System requirements for LINE

• The current version of LINE requires iOS 17.0 or later
• "Although not recommended, you can use older versions of LINE" "up to LINE 15.7.2" "with iOS/iPadOS 16.0 to 16.7.12". With a warning: "Be advised If you don't update the LINE app for an extended period, you may not be able to restore data such as your chat history."

I suspect that

• There is no way to download an old version of LINE from the App Store if you are a new LINE user.
• Despite the claims that you "can use older versions of LINE" with iOS 16, something may have changed with the LINE service that caused those old versions to become completely unusable – not "just" to nag you to install an update that your iPhone 8 Plus is too old to support.

I contacted the developer and all they can suggest is to buy a new phone.

If the developer is saying that they won't support you on iOS 16, then your options are

• To buy a new phone,
• To try to use the Web interface to LINE in a mobile browser like Safari (which may or may not work), or
• To go without the use of LINE on your phone.

Line is not an Apple product. Contact the app developer here --> App Support or Line Help Center