Hi @Kateryna in order to show the multi ref categories, you have to drop a collection list in and then bind it to that multi ref you’ve assigned for the post.
The reason the multi ref doesn’t show is that you’re trying to bind it to 1 single text block, when you need to display multiple, hence the collection list.
It’s a really quick process and you’ll be sorted in minutes 
- see screen shots below.
Hope that makes sense.