Understand how Cloudflare integrates with Google Analytics.
Cloudflare proxies traffic to your origin web server. Therefore, the Cloudflare connecting IP matters only for any programs that read logs directly from your web server (like awstats).
Disable Ad Blocker plugins in your web browser when when enabling the Google Analytics App for your Cloudflare domain. Otherwise, you will observe a generic error when enabling the Google Analytics App:
Error An error occurred.