Questions?

I need to send response info to Funnelytics. Typically I would do this in GTM with a custom HTML tag but I can't work around outgrows iframe. Do you offer a javascript API? Or do you have recommendations for writing custom events to the parent container in GTM? I'm looking to listen for a payload on submit of a form and send outcome information to Funnelytics.
https://help.funnelytics.io/en/knowledge/adding-funnelytics-action-script-to-gtm-to-track-customer-events

Any help is appreciated.