Please visit the wiki for the most up to date information. If you are making requests to endpoints that are not plurals, then you fall under this category. You need to update your application to use the new API urls and response formats.
As the result of no shared code between the old and new site, the API changed, both in response format and urls. We updated our codebase quite drastically in March 2020. There are a few different reasons that you can run into this message:
It's great, and probably does what you want!
403 Access Denied - Oh no! If you were using a script/program you found to try and download content, it's likely that the script was what resulted in your request being blocked.
