The “API keys” section you mention handled the keys for our legacy API, which we’ve been in the process of shutting down for the past year or so. At the beginning of this month we retired it completely, and with it we removed the API keys menu and the functionality behind it. For the past several months use of those API keys had been severely limited.
@unlockdesign has pointed you to the instructions to get a token for the modern API. Those tokens are required to interact with our APIs now. Prior to the legacy API retirement, we communicated with authors to make sure their items had been migrated to the new API.
If you’re using an item that still uses the legacy API, please first try to update it to the latest version. If it is already the latest version, then please get in touch with the author. They should be well aware that the legacy API has been shut down now.
Let me know if you have further questions about it.