action-xhr tag is missing

Hi folks,
I am facing an error in my amp result regarding the STC form. The amp tester gives the error “The mandatory attribute ‘action-xhr’ is missing in tag ‘form’.” and I think this is maybe due to the action attribute is missing in the HTML of the form. Whatever is the reason I need to know how to fix this error.
Any help would be really appreciated.
Thanks in advance.

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