Synonyms are hard to set up and do not always work really well. Here is how you set them up in any case:
Use the → check box to see the synonyms tool.
Select first word (A) you want to make synonyms, then click on the second word (B).
The button in the synonym tool changes it's text to .
The words will now be shown as connected in the synonym tool and can be recognized as synonyms in the practice.