I'd like to revive my iPhone and update to the latest version of iOS

Finally resolved!

I installed the official app 'Apple Support' on my iPad and I succeeded to contact the official support.

Still I don't understand why I cannot use 'Get Support' on my safari browser, anyway.

My iPhone turned recovery mode with my Mac, and my iPhone revived and the latest iOS is finally installed.

Thank you very much for your kind replies, deggie!!! :)

Although the language of the original sentense is Japanese:

アクティベーションエラー

アクティベーションを完了できませんでした。

iPhoneを復元して最新バージョンのiOSをインストールしてからもう一度アクティベーションを実行してみてください。

問題がそれでも解決しない場合はカスタマーサポートにお問い合わせください。

In English it means:

Activation error

The activation could not be completed.

Please restore your iPhone, install the latest version of iOS, and then try activating again.

If the problem still persists, please contact customer support.

-------------------

It says me to install the latest version, but the setting must be completed to install it.

How can I do?

Thank you for the comment!

Yes, the SIM is in the iPhone.

The version is 9.3.

When I click "Get Support", now I see the message "403 Forbidden Apple",

though yesterday morning I succeeded to access only once.

Do you see the page?

Via my computer the message was the same, "Activation error ...", which I saw on the iPhone.

I'm using Mac OS Big Sur, version 11.2.2, so I don't have iTunes.