Americans Abroad

In what manner did they say this to you?

The reason I ask is that it seems odd that they communicated to you in some way, but you need someone else to call them back.

If you it is merely a booking agency and the actual rental is from Avis, then, no, you do not need an international license to rent from Avis in Europe if you have a US license.

However, if you are looking at a general information webpage then, sure, it will say that, since many rental agencies require one to rent to people from various countries other than the US.

But your post is not really clear on whether carjet is simply a booking agency and your rental is through Avis, nor is it clear whether they told you, specifically, that you need an international permit, or if you are just reading general information that they have posted somewhere.