ChatGPT Plus is listed at $20 per month, but the actual price you pay can vary...

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

ChatGPT Plus is listed at $20 per month, but the actual price you pay can vary from about $13 to $27. This difference happens because of extra costs like VAT or GST taxes, or the fees app stores charge on iOS and Android