spining loader and email not sent resolve issue please read!!

any one having issue with contact form sending email please read!!
after few day battle with issue thank you for plugin developers they give no help to this issue support are useless here
shortly i explain what was my problem and how i fix.
my contact us form stop sending email and spinning loader keep turning no success msg display I have did few test to see if problem from server side but it’s not all fine then change theme didn’t help then uninstall plugin freshly install still no luck deactivate all plugins to see if any conflict still no hope then from chrome I look at source to see i can see something i sow wordpress rest-api giving 404 eror
earlier i disable rest-api with .htaccess I enable again did test you know what all worked.
simple think cause problem developers should make simple post for people can read what can occur in relation to plugin

hope this can help to people looking for a solution