Test Donation displays "this site is a non-secure"

Hi – We do not have an SSL Cert on our site, however I did not think that was necessary as we are making the donation via Paypal. So if we are making a donation on the Paypal page, why would we get the message
right at the end that says this site is a non-secure site, are you sure you want to send?

Thank you! Elysa

https://www.ads-software.com/extend/plugins/paypal-donations/