For everyone that´s not in fear of a little copy & paste work, here´s a short tutorial that explains, how to create a customizeable tab (Custom Tab)
The whole process doesn´t take longer than 20 minuntes and you´ll be able to have your shiny shop beeing fully operational for your fans:
it didnt work. i did until the end, and it said only facebook page with like more than 2000 is allowed to use this tab. LOL 
I reproduced that error “successfully” Which, is strange 
In Feb 2019 I managed to make it work seamlessly for a page that only had 300+ users
Which is also confusing to me, as the “2000 users” rule seems to be in place since late 2018
see this article: https://help.powr.io/hc/en-us/articles/360003062354-Facebook-This-page-does-not-have-permission-to-install-the-custom-tab-error
To be honest, I have no idea yet how to tackle this issue for pages with less users.
It´s probably worth researching some more DEV forums.
This I believe is a change that has been made to the Facebook API. A similar thing happened to me with my Fine Art America Print On Demand Account; and FAA support told me that FB is no longer allowing for store integration on the platform.