Paypal validation troubles

I’m using the paypal-ruby plugin and I have it all working – except
the validation of the IPN. I get the post from payal, and it gets
posted back to PayPal for verification by the plug code, and it all
looks right to me, but PayPal returns INVALID. Has anyone else seen
this or have any tips for what to look for?



I haven’t used the ruby paypal stuff but I tangled with that in java.

I know that paypal says you have to post the params back to them
exactly as you got them (watch out for charset issues)… that and you
have to add the “cmd=_notify_validate” param… you’re doing that right?