Problem with CC Library collaboration

Hello,
I've created a CC library with paragraph and character styles in InDesign and want to collaborate with two colleagues (probably more in the future).
In InDesign, I clicked on "Collaborate" in the panel options and put in their e-mail addresses (for reading and editing).
I've only tried it with one colleague so far. However, when she clicks the link in the invitation e-mail the screen that shows up in her browser doesn't show my shared library.
She logged out and in again, cleared her browser cache and restarted it, it didn't help. It doesn't show up in her InDesign libraries panel either.
We both have the Creative Cloud CC 2019 installed, but I have a Middle Eastern version – could that be the problem?
Any help is appreciated!
Best,
Anneke