WP Fastest Cache is totally compatible with Cloudflare. In order to minimize potential conflicts, you need to Cloudflare cdn integration.
This integration has two important goals. Firstly, this integration prevents incompatibilities that may occur between Cloudflare and WP Fastest Cache by changing some settings of Cloudflare. Secondly, purging cache of Cloudflare cache as well when the cache is cleared via WP Fastest Cache.
How to Find API Key
1. Go to https://www.cloudflare.com/a/profile
2. Click on “API Tokens” tab
3. Click on “View” and copy the Global API key