@apeksha-barhanpur

My apologies, I mistakenly believed you had a support plan with FusionAuth (let me know if I am mistaken).

Regarding your question --

Have you had a chance to review the troubleshooting guide that we publish for email?
https://fusionauth.io/docs/v1/tech/admin-guide/troubleshooting#troubleshooting-email

Lastly, a good tip is to remove FusionAuth completely from the email equation by using SWAKS. SWAKS will complete an email exchange with just your email provider credentials (thereby removing FusionAuth from the equation). If SWAKS fails, then would offer good troubleshooting information.
http://www.jetmore.org/john/code/swaks/

Thanks,
Josh

@adam-0

It might be good to make sure that you are not mixing up the registration and the email verification flows (not sure if you are or are not).

https://fusionauth.io/docs/v1/tech/tutorials/gating/gate-accounts-until-user-email-verified/#troubleshooting-email-and-registration-verification

This guide will walk you through the admin UI side of things but, the corollary to the API is the same.

Thanks,
Josh

No, this is not currently possible. Here's an open issue, please upvote it if this is a crucial feature: https://github.com/FusionAuth/fusionauth-issues/issues/1082

One alternative to repeating content would be to use some kind of generation system outside of FusionAuth (freemarker, handlebars) to generate text files. Then you'd then upload as the email templates via the API.