The domain www.iotplayground.tk is being served through Cloudflare CDN. Any Let's Encrypt certificate installed on the origin server will only encrypt traffic between the server and Cloudflare. It is strongly recommended that the SSL option 'Full SSL (strict)' be enabled.
https://support.cloudflare.com/hc/en-us/articles/200170416-What-do-the-SSL-options-mean-
Requests made to the domain
Request to: www.iotplayground.tk/2606:4700:3033::6815:3f03, Result: [Address=2606:4700:3033::6815:3f03,Address Type=IPv6,Server=cloudflare,HTTP Status=521], Issue:
Trace:
@0ms: Making a request to http://www.iotplayground.tk/.well-known/acme-challenge/letsdebug-test (using initial IP 2606:4700:3033::6815:3f03)
@0ms: Dialing 2606:4700:3033::6815:3f03
@186ms: Server response: HTTP 521
Request to: www.iotplayground.tk/2606:4700:3035::ac43:a8f3, Result: [Address=2606:4700:3035::ac43:a8f3,Address Type=IPv6,Server=cloudflare,HTTP Status=521], Issue:
Trace:
@0ms: Making a request to http://www.iotplayground.tk/.well-known/acme-challenge/letsdebug-test (using initial IP 2606:4700:3035::ac43:a8f3)
@0ms: Dialing 2606:4700:3035::ac43:a8f3
@186ms: Server response: HTTP 521
Request to: www.iotplayground.tk/104.21.63.3, Result: [Address=104.21.63.3,Address Type=IPv4,Server=cloudflare,HTTP Status=521], Issue:
Trace:
@0ms: Making a request to http://www.iotplayground.tk/.well-known/acme-challenge/letsdebug-test (using initial IP 104.21.63.3)
@0ms: Dialing 104.21.63.3
@176ms: Server response: HTTP 521
Request to: www.iotplayground.tk/172.67.168.243, Result: [Address=172.67.168.243,Address Type=IPv4,Server=cloudflare,HTTP Status=521], Issue:
Trace:
@0ms: Making a request to http://www.iotplayground.tk/.well-known/acme-challenge/letsdebug-test (using initial IP 172.67.168.243)
@0ms: Dialing 172.67.168.243
@208ms: Server response: HTTP 521
A and AAAA records found for this domain
www.iotplayground.tk. 0 IN A 104.21.63.3
www.iotplayground.tk. 0 IN A 172.67.168.243
www.iotplayground.tk. 0 IN AAAA 2606:4700:3033::6815:3f03
www.iotplayground.tk. 0 IN AAAA 2606:4700:3035::ac43:a8f3
Challenge update failures for www.iotplayground.tk in order https://acme-staging-v02.api.letsencrypt.org/acme/order/5751349/966981
acme: error code 403 "urn:ietf:params:acme:error:unauthorized": Invalid response from http://www.iotplayground.tk/.well-known/acme-challenge/pXwsUP2juwMFKhgoqVZ-8l-Vuwt_JyoNhi-EUKQ5GDo [2606:4700:3035::ac43:a8f3]: "<!DOCTYPE html>\n<!--[if lt IE 7]> <html class=\"no-js ie6 oldie\" lang=\"en-US\"> <![endif]-->\n<!--[if IE 7]> <html class=\"no-js "