ChatGPT Plus has a listed price of $20 but the actual cost you pay can vary...

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

ChatGPT Plus has a listed price of $20 but the actual cost you pay can vary between $13 and $27. This difference comes from taxes like VAT or GST and extra fees added by app stores on iOS and Android