OpenAI is not accessible in some countries, and that includes all its services like ChatGPT and its API. You can bypass this block by making yourself appear to be in a different country with a VPN.
All you have to do is turn on a VPN app on your device and connect to a VPN server location where OpenAI is available. You’ll no longer be blocked based on location. However, OpenAI might also require you to provide a phone number from the country you’re trying to appear to be in so it can send you a verification code.