JAmp now supports a more advanced forms management thanks to the integration with:

Contact Enhanced - https://idealextensions.com/joomla-extensions/component-contact-enhanced.html

Read more here: https://idealextensions.com/joomla-extensions/component-contact-enhanced/documentation/59-integrations/165-compatibility-with-amp-accelerated-mobile-pages.html

Google AMP forms have several limitations that may prevent the normal working behavior of the form, for this reason has been developed a specific integration with Contact Enhanced.

Take care to activate the parameter 'Enable AMP form' under plugin settings and use https on your website. Https is required in order to use forms with AMP otherwise it will not work if your website doesn't have a valid SSL certificate.