Problem when linking via Facebook

iPAD, Facebook app.
When visitors are in the Facebook app and click on a Facebook link on my Facebook page, they go to my website post of an app I posted there. When they then click on the buy link, Facebook opens a ‘about’:blank’ page. So no linking towards the app store, but an empty page.

This is my FB page:
https://www.facebook.com/Airlinecrewdiscount
Click on a app promotion (When using iOS Facebook app on an iPAD) and then you can see what I mean…

https://ww.wp.xz.cn/plugins/app-store-assistant/