Challenge self check failed for domain

[inspiredearth]

So far I've been unable to get this plug-in to work on any site I've tried it on. Usually the catch is this error, "Challenge self check failed for domain ... "

What's the cause of this, and how to solve it?

[justdave]

Could be any of several things. Many of them are discussed here: https://wordpress.org/support/topic/errorchallenge-request-failed-for-domain/