can you share step by step how you do this?
I use an android phone, so I don't have idea how the iphone Facebook app works or looks.
Login on your Facebook app, navigate to pages and select the page you want to add story and link to.
once open.
On the homepage of the your facebook page.
Under the cover photo is your page name and to the left of the page name you'd see the Facebook page profile picture with '+' sign. tap on it and the first option should be 'create story ' also tap on this.
Select the picture you want to add to your story and tap 'NEXT' at the top right corner of the screen, you'd be presented with a preview of the picture where you'd edit it to how you want your story to appear. On the top right corner of this preview page, you'd see the link icon. Once tapped on, you'd see an input box tagged 'custom link' paste your link in that input box and tap 'add' at the top right corner.
After doing this you should be taken back to the preview page with the link icon now highlighted with white background or something like that.
you can then tap 'your story' which is at the bottom of the screen if you want to publish your story or you do some other changes you want.
that's it.
While writing this short tutorial, I tried this on smaller pages that have even zero fans and it worked. So this is a guaranteed method to add Link/URL to your Facebook page stories.
Good luck, by the way this generates a reasonable amount of traffic from my 84k fans page daily.