Elias here with Shopify Support. Thank you for reaching out.
I understand you're trying to verify your domain with Facebook using the Meta-tag Verification method. Can you confirm where you've saved the link on your site? Also, did you remove the password protection for your online store before verifying?
If you're not sure where to place the link for the Meta-Tag Verification from Facebook, you can simply paste the line of code into your theme files ('Online store > Themes > Actions > Edit Code'). From there, look for the Layout folder and locate the file - theme.liquid. When pasting the code in an empty line or on a new line, it's important to paste the code after the opening <head> tag or before the closing </head> tag in the coding. Once that's done, remember to disable the password protection for your online store and you can try verifying your domain with Facebook again.
Here's an example from my test store:
Let me know if this can help you verify your domain with Facebook! If you have any other questions, don't hesitate to let me know!
Thank you for following up!
While there isn't a way for me to verify the steps you've taken, as I don't have enough information at the moment, we also lack the ability to authenticate merchant accounts over the Community Forums. However, this is something that our Support team would be happy to assist you with this through live chat, email, or callback. Please visit the Shopify Help Center and log in to your account to create a support request.
I hope this points you in the right direction to get help with verifying your domain with Facebook. If you have any other questions, please don't hesitate to let me know!