The API is an exclusive feature of our Pro plan. You can generate API keys in your account settings:
Click on your profile icon and go to Account.
Click on the API tab.
Or simply go to https://rss.app/account/api.
Here you'll see the API key generator and the number of monthly API operations. Keep in mind that operations reset every month.
To replace an old API key, just press Generate API Key again; the old key will become invalid.