I am trying to integrate Alertpay into my TE. When trying to generate the code, they ask for an Alert URL.

Can anyone tell me what this is?

It is probably your referral id.

The alert url is the email address you set up at alert pay for your traffic exchange, once you have done the email address part there should be a drop down box in Set Up alert URL Associations.
Select the correct email address and proceed from there.
They also ask for the IPN alert link
In that area put http://yourdomain.com/alertpay_ipn.php

That is how I did it for a ventrino exchange and if you are using ventrino when you add the encrypted security code you must replace any + in the encrypted security code for spaces otherwise it will not work.