503/1001 error

Hey,
I have changed my DNS provider for my tech business right now. I set up the DNS, and it is working fine. However whenever I try to turn on proxy I get a 503 error on the browser and 503(1001) on built-in speed test. What might be the issue, it happened to same site with two different hosting providers. Only happening to this domain name weirdly.

Cheers,
Berk.