Can't purge CloudFlare cache

I have the same problem as the two commenters at https://ww.wp.xz.cn/support/topic/cannot-purge-cloudflare-cache-please-enter-cloudflare-e-mail?replies=3.

I have my CloudFlare account email entered, but every time I click Purge Cache, a JavaScript alert says “Please enter CloudFlare E-Mail.”

I am getting this error on all 3 sites I’ve tried. Two are on an InMotion Hosting server, the third is on GoDaddy (theportalrockopera.com). I am using the latest versions of WordPress and W3TC. Please advise.

https://ww.wp.xz.cn/plugins/w3-total-cache/