Michael is right... need one-by-one query each related data. And use dummy (backup) databefore real migration..
just FYI 🙂
My personal opinion, this is most powerful migration tool ever made for Flarum to accommodating MyBB user like me. I've been trying before. Since my forum is huge 1-2 million posts, I decide to manually one per one converted (manually). Not using this extension.
Mostly, converting tool is easily working for small/medium size of MyBB.. But, for big forum it will create some "time-out" behavior or others unpredictable results. Server skill is also needed for this case..
If you need convert.. First: Category (Tag), sub forum, then continue with bigger size such users and finally posts it self.. Please comment-out the procedure inside this script (need PHP skill), one by one before continue next step.
I keep my old forum for archived purposes. Both exactly same (Flarum, MyBB, PHPBB and SMF) 🙂