I'm having the same issue, and it's 3 months after you (and others) have had the SAME issue!!! Maybe if we start blowing them up on their own site we will get a response!! I was able to chat with someone in messenger but after an hour chatting with them they were useless!!! If I don't get anywhere in the next 72 hours I'm gonna get thrown off FB cause of the posts that are coming lol.
I do exactly the same in the business manager when i try to verify the domain.myshopify.com but even adding the dns verification in the header the verification is still failing.....do you know why is this happening?
And i already look the entire code and i cant find the second <head> just have the </head> sos please!!