I have been using Copilot for a long time. Yesterday I changed my GitHub password and started getting this error in Copilot:
Invalid copilot token: missing token: 403
I tried logging in and out and reinstalling the IDE, but unfortunately I didn't get any results.
I tried closing and reopening my account and restarting the IDE.
There are multiple reasons this could be happening.
The most basic thing to check first is that you've actually properly followed all the steps for setting up GitHub Copilot usage. You can find such docs on VS Code's docs site and on GitHub itself. Those steps include installing the VS Code extension, authorizing VS Code in GitHub, and activating your free trial / paid subscription.
If you don't have a GitHub Copilot subscription, then you can sign up for one by following the steps in https://docs.github.com/en/copilot/quickstart#signing-up-for-github-copilot-for-your-personal-account. For personal accounts, TL;DR go to https://github.com/settings/copilot and click "Enable GitHub Copilot", etc.
It could be due to an error connecting to the GitHub API to request a token for GitHub Copilot usage. You can request another token by signing out and then back in to GitHub Copilot from VS Code. You may or may not need to revoke VS Code's access to your Github from Authorized Apps before trying to sign back in to GitHub Copilot in VS Code again.
The docs for troubleshooting authentication issues say to sign out of your GitHub account in VS Code, reload VS Code (using the Developer: Reload Window command in the command palette), and then sign back into your GitHub account in VS Code.
If you use multiple GitHub accounts in VS Code, you might need to do some sign-in sign-out dances (source).
It could be due to trade controls (country things / region-based restrictions). See https://docs.github.com/en/site-policy/other-site-policies/github-and-trade-controls for more info.
It could because of a bug in GitHub Copilot or a deployment mistake. Ex. https://github.com/orgs/community/discussions/47577#discussioncomment-4998002, https://github.com/orgs/community/discussions/47577#discussioncomment-5079299, https://github.com/orgs/community/discussions/40019#discussioncomment-4234433, and more examples on https://www.githubstatus.com/history. If it's a non-server-side bug, it might be fixed in the pre-release channel of the extension, so you could try switching the release channel.
If you're the kind of person who likes reading things to try to find a solution before asking for help, you could try combing through a google-search of "site:github.com "Invalid copilot token: missing token: 403"".
Someone in the comments here said they got this error because they meant to use a different GitHub account and were using the wrong one.
If none of that works, then you can reach out the support team on their support page. If you end up finding out some info that could potentially help others, please come back here and post an answer post about it.