Tried to order pizza from Dominos and I can access the site, but the icon to login does not work.
I whitelisted the dominos.com and www.dominos.com, also used wildcard and Rexfilter, still doesn't work.
The only way it works is by disabling Pihole. So, something in Pihole is blocking some features from the website but I can't tell what it is.
I thought whitelisting a site would bypass Pihole... why is Pihole still blocking this site?
Handy tip – access a known domain before and after your test. You can then easily find these in the Query Log and know that the answer is somewhere between the known domains.
Example
Go to start.example.com in your browser. The site won't work, but that's okay, the point was to make Pi-hole look it up so it's in the Query Log. Your browser may also silently try a variant like www.start.example.com, so that will appear too.
Now visit Dominos and go through the order that fails.
Now visit end.example.com in your browser.
Now go to the Query Log and look for the start domain and end domain. The Dominos lookups must lie somewhere between them. There might be other stuff there too, related to other stuff on your network, but it helps to narrow down where to look. By using two different domains you ensure that each one will be looked up and appear in the log.
That is a known tracking domain and appears in a lot of ad lists. You could whitelist it so that Dominos is working, and then go into Domains, find it at the end of the list and flip the green Enabled switch to Disabled.
That will disable the whitelist entry for that domain, so it will be blacklisted by default once again. And while you're in there, add a note like "Enable for Dominos" to remind you why it's there.
That way Pi-hole will protect you from it during normal use, and when you want to order pizza you can temporarily allow it, place your order, then block it again.