Chat GPT servers status: status.openai.com
Depending on your location, ChatGPT (GPT-4 and newer models) might sometimes be inaccessible either due to infrastructure issues or because OpenAI is running a major update that disrupts the chat (integration of a new model, GPT-5, new features, new UI).
If you really need to access ChatGPT and can't wait for OpenAI to fix it, here is a clone you can use for free (up to ~10 requests) with GPT-4o and the same features (file uploading, chat history, attachments, OCR, image generation, DALL·E, etc.):
GPT Workspace (https://app.gpt.space)
GPT Space is an alternative client to OpenAI's chat interface, ChatGPT. It relies on the same models and can be used as a backup anywhere in the world. It is hosted on servers all across the globe to ensure continuous availability. You will have access to other features like GPT Workspace Google Docs AI, GPT Workspace Google Slides AI and GPT Workspace chatGPT for gmail.