Can't link to Facebook anymore

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I'm trying to install Shopify onto my work Facebook page. We were linked previously but I thought I needed to upgrade using the new Shopify app.
I'm admin on my work Facebook page and in business manager. I'm trying to the link the two but to no avail.  I can't find a way of granting permission to link business manager on the main facebook page to join the two - I've followed the instructions. There is no request to approve the link.
Facebook aren't replying to any of my emails/ queries.

Shopify snip.JPG