ChatGPT Plus lists for $20, but actual prices vary from around $13 to $27...

https://www.slideserve.com/aaron_ward92/why-does-chatgpt-plus-cost-more-on-android-than-on-the-web

ChatGPT Plus lists for $20, but actual prices vary from around $13 to $27 depending on your location. This happens because taxes like VAT or GST get added, and app stores on iOS and Android often charge extra fees