Wine Sellers Direct - Market Hall review for Google & YouTube

I was told I can set up Sub Accounts in Merchant Centre using Advanced Merchant Centre accounts, so I can then have and isolate my second and subsequent stores even though the domain remains the same but it might be markethall.domaain.com.au I have one business account with Google, that all my connections are linked for Ads, Merchant Centre, Analytics, Business Profile etc. I received advice I need to add an email address to the sub account in merchant centre which I have tried, but it says this email is already associated with this account. When I deleted the app and links to try again it keeps creating new businesses in my Merchant centre but I can't do anything with them. I can't create a google account for my boss as to sell on Merchant Centre you have to be approved particularly selling alcohol and now I am stuck with a website I have built and no way to link it to google even though this process should be seamless. My original account now says I need to verify my domain, but this has been done?? and I have it still connected via the app for my original store. Help please.