Go to Settings > APIs > API Keys and put the following into the "CurseForge Core API" box
$2a$10$bL4bIL5pUWqfcO7KQtnMReakwtfHbNKh6v1uTpKlzhwoueEJQnPnm
If the API key changes, it may be found again with this guide
curseforge has patched the method previously used to find the api key

the guide by dev of pollymc is obsolete because the thread has been deleted