I read on here that someone had managed to do this, but I don't really understand the process.

I have Custom Records pre-created via a workflow and an online form that customers can fill out to update the Custom Record. This is done via seeded links and pre-populating form fields so records are never duplicated.

What I want to do is, when a certain field on my online form is checked/made true I want it to trigger the creation of a Sales Order. However, whenever I try and create a script, I can't get it to do anything. If I attach the script directly to the online form, it doesn't work, I just get an error which I believe has something to do with form users having inadequate permissions to certain API's. When I attach the script to the Custom Record, it can't trigger because there's no option to trigger on Update from a Online