Prompt Title: Canvas Integration with PHP.

If you're getting an "invalid access token" error when trying to access the Canvas API using your developer key as the access token, there are a few things you can try to resolve the issue:

1. Make sure that you're using the correct access token. Double-check that the developer key you're using matches the one that was generated for your account in the Canvas settings.

2. Verify that the access token has the correct permissions. Make sure that the developer key has the appropriate scope to access the resources you're trying to retrieve from the API. For example, if you're trying to access the courses API, the developer key should have the read:courses scope.

3. Check the syntax of the API request. Make sure that you're constructing the API request correctly and including the access token in the Authorization header of the request. You can refer to the Canvas API documentation for guidance on constructing requests.

4. Check that the API endpoint is correct. Verify that you're using the correct API endpoint for the resource you're trying to access. For example, the endpoint for retrieving a list of courses is /api/v1/courses.

5. Test the access token with a different API endpoint. Try using the access token to access a different endpoint in the Canvas API, such as the user API, to see if the issue is specific to the courses API or a more general issue with the access token.

6. Check for other errors in the response. If the response from the API includes additional error messages or status codes, they may provide more information about the issue.

If none of these steps resolve the issue, you may need to contact Canvas support for further assistance.