ipn paypal is necessary??

[francota]

Hello
I have some problem with payment by paypal, infact i receive an email that say to look into file paypal.2.log.php.
In that file there is this log:
2015-07-14 15:53:51 ERROR validateIpnContent: Invalid IPN validation: NO ANSWER FROM PAYPAL

But i dont understand the configuration of IPN on my account paypal is indispensable??

Thanks
FRank

[francota]

If it is necessary where can i Find how configure IPN for VM3??

Thanks
Fank