PayPal responded with http code 400

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Help,
I seem to be having issues with PayPal and processing of orders. I get an error in the logs stating:

And then an email from PayPal with the error stated as:

I have tried adding the IP address and removing all the IP addresses, but nothing seems to work!

Please help this is affecting a live site!

Thanks
Lee

Hi,

The error indicates that the IPN was rejected because the IP is not in the list. So yes, removing everything from the IP setting is what I would recommend. That will also prevent a similar issue in the future.
There is already a security in the way the system works. Checking the IP addresses is not necessary (it can be nice to have as extra security but you need to actively update the list when PayPal adds new IP addresses).

You won't get the same error if you remove the IPs from the setting in the payment method. If you still do, then maybe you have several paypal payment method and you changed the setting of another one than the one you were using in your test or something like that.