Hiya
I am having the same problem. I have tried verifying my Facebook Business account by adding a line of code into the section of my theme.liquid but Facebook tells me it cannot verify even though I can see their required bit of code in the source. My other option is to upload an .html file to the root directory which is not possible as they look for a .html file and I can only create a .liquid file.
Have you come across this issue of not being able to verify elsewhere?
Many Thanks
Goliath Merchandising