The ChatGPT iOS mobile app is currently available in the countries listed on the ChatGPT Supported Countries article.
If you are an existing ChatGPT user, please log in with the same authentication method (username and password, Google, Microsoft, or Apple). When you're ready to subscribe to ChatGPT Plus or ChatGPT Pro there are a couple options.
Upgrading to Plus or Pro
Option 1: Upgrade on the web
Go to chatgpt.com, click on your name from the top right corner of the screen which will then display a popup with upgrade options including an Upgrade your plan option with options for either Plus or Pro.
Option 2: via the iOS app
There's a couple ways to upgrade from the iOS app.
The easiest way is, from the top middle of the app, click Get Plus or Get Pro to open the upgrade menu then click Upgrade to Plus or Upgrade to Pro which will take you to the Apple subscription payment page to confirm:
The other way to upgrade to Plus from the iOS app is clicking the two horizontal lines in the top left of the app to open the chat history & menu -> click on your name to open Settings -> under Account click Upgrade to ChatGPT Plus or Upgrade to ChatGPT Pro.
For new ChatGPT subscribers
If you've downloaded the iOS app from the App Store but find the subscribe button grayed-out (light purple), this indicates that Apple is still in the process of activating the subscription feature. The message above the button will read, "In-app purchases are currently unavailable. Please try again later". This activation may take up to 48 hours. We appreciate your patience during this time.