ChatGPT Plus is listed at $20, but the actual price you pay can range from $13...

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

ChatGPT Plus is listed at $20, but the actual price you pay can range from $13 to $27. This difference is mainly due to taxes like VAT or GST and fees added by app stores, especially on iOS and Android