Hey there @skrama87 !
The syntax you have attached results into a an alternate checkbox. - [>] Moved/Forwarded.
The correct syntax for callouts are something like:
> [!celebrate]
> Let's party!
or
> [!tip]
> This is a tip!
You can visit this link for the official how-to for callouts! Whatever is in there should work with Primary 
Hopefully this answers your question? Let me know if these worked!