If you are using windows, try this with the input HUD display so you can check if your input is clean
There is no secret to it except doing it clean and fast.
This is the street fighter 2 engine, shit does insane damage so srk isn’t supposed to come out easy (it’s easier than SF 1) if you dont do it fast.
The Z motion and forward then fireball are essentially the same.
It’s just a twitch once you get used to it.
There is another way to do it, from crouching position, as explained by XSPR in this pic
You start at red and do a small 360 circle back to where you started.
I personally find it way easier to do Z in 1p side and small circle in the 2p side.
Z is easier to combo from standing fierce and small circle is easier to combo from crouching low forward.
BTW there are also some beginner to intermediate players on ggpo. Playing the CPU is also fun when you just want to practice your SRK on reaction.