To add on to this some of the Quick Base help documentation actually has the wrong header listed. The one they have listed will give you no real error but the webhook will just fail to fire and leave you scratching your head. I've reported the ones I've found in the past but more still might be out there. The way Nathan suggested is the right way.
Looking at the webhook above it looks like the user token is malformed. I would not expect to see a token like that. My user tokens are always similar to a random string like this one I just made up "fls45t_gfgf5hgh_hrteh453y5yu546". I also don't wrap mine in percent signs, so that may be another issue. I would verify you are using the right user token. If it is correct then that is a brand new format for them or at least one I have not seen yet.
Looking at the rest of the webhook you might be running into an issue with "[Old.Status]->[New.Status]" I would expect to just use [Status] here. If for some reason it isn't the newest Status(I don't see why it wouldn't be) you can look into other options. Just go simple for now.
