Supplier Registration Page customization to invoke external API

Summary:

Supplier Registration Page customization to invoke external API

Content (please ensure you mask any confidential information):

We have a requirement to invoke the external API from Supplier Registration Redwood page to validate the Tax registration number on tabbing out of the Tax Registration Number field or on click of save button.
I don't see any Action Chains when I edit the page in VBS, I could find the the event "submitActionEvent" but there is no event listener or Action Chain built on it. If I build the custom Action chain I can raise the event but I won't be able to stop the save/submit.