Defer the referral email until some time has passed. Also include some incentive to refer somebody.

ppg

This was my reply to the referral email:

I could refer, but I have no incentives to... and haven’t really tried the app yet, so no. Come back with a value proposition and I might want to.

And this email should come at least a few days later, not now. 

6 months free, extra scans, etc you name it.

ppg

Referral email should not come in the first day.

Any marketing sensible person would know that