So I finally got around to documenting this because I kept running into the same issues over and over (you know how it is, you set something up, it breaks six months later, you forget what you did) and Cloudflare registrar (which is nice for cost, I will give them that, no markup on renewals is genuinely refreshing in this industry where everyone wants to squeeze you) has these weird gaps where they support some DNS providers but not others and the documentation (ha!) is either wrong or missing the edge cases that actually matter in production (like when you have a domain that was transferred in and already has glue records that don't match their expected format and the UI just silently fails or gives you this generic error that means nothing) so anyway the main gotcha is that if you're using external DNS (not their own, which is fine, I prefer Contabo's anycast setup for my own reason
