I’m trying to understand how Webflow’s form success message triggers when working with external form processors.
For instance, working with Mailchimp triggers the success message on submission, whereas working with some other form processor does not (even though the other one returns a code 200 Success on submission).
Mailchimp is officially supported and is handled by the Webflow code, when you use an action that is not supported by Webflow the form will not be sent at all by Webflow JS, so you will need to code that functionalities on your own
For unrecognized webhooks, you can make Webflow’s success/fail form responses work with some scripting. My Webflow Utils (WFU) library has a handler which supports three webhook providers;