Verify work email with an OTP

I have been working on a website, where work email is an important part of the website. But due to some restrictions, we can not make official email verification mandatory.

Currently, OTP will be sent to the provided work email and which has be entered to verify.

It is a non mandatory field. Currently, we added a button "Send OTP to verify" just after work email field followed by a field "Enter OTP", but the conversion rate is less than ~4% of users that verify the email.

We also used popup for Entering OTP, but those are not good Idea as per conversion is concern .

Any help??