Loopy Pro: Create music, your way.
What is Loopy Pro? — Loopy Pro is a powerful, flexible, and intuitive live looper, sampler, clip launcher and DAW for iPhone and iPad. At its core, it allows you to record and layer sounds in real-time to create complex musical arrangements. But it doesn’t stop there—Loopy Pro offers advanced tools to customize your workflow, build dynamic performance setups, and create a seamless connection between instruments, effects, and external gear.
Use it for live looping, sequencing, arranging, mixing, and much more. Whether you're a live performer, a producer, or just experimenting with sound, Loopy Pro helps you take control of your creative process.
Download on the App StoreLoopy Pro is your all-in-one musical toolkit. Try it for free today.

Comments
The only way that can work is if the synth provides midi mapping to that function or if it exposes an AUv3 parameter. I don't recall any synths that do expose their MIDI panic button, but I may just never have noticed.
However, there's a standard MIDI "all notes off" message that some synths may respond to: MIDI CC 123 with value 0. If it's an MPE synth, you probably need send it once for every MIDI channel.
If you're getting stuck notes when stopping clips then there's something wrong in Loopy Pro and it would be good to report the details of when it happens.
LoopyPro always sends all Note Off correctly !
It is the AUV3 plugin "iBassist". A wonderful
musical tool, also sends a bass line via MIDI,
but unfortunately very buggy.
But now I have found a workarround:
I switch all synts off and on, with my
Stopbutton.
CC 123 / value 0 is a good thing to try sometime, if only to know which synths respond to it.
Yes, sure, that's an elegant solution too, thanks.
Just to be clear: I meant this button, not the one in the plugin
Ahh. I misunderstood. I don't believe there's any way to trigger that with an action.
While there isn’t an action for that, try sending midi cc 120 value 0 (all sound off) as well as message wim mentioned (all notes off)