ExpressionEngine 2.4.0 Store 1.6.4
We're having issues with Paypal as when the browser goes back to the checkout page from Payal we get the "Invalid response from payment gateway." message and the Store 1.6.4 cart doesn't record the transaction. Paypal, however, does send out an e-mail to the client and we receive payment. Any thoughts on what could be the issue? This has only been happening within the last 4 months.... Site has been running since August 2012.
PayPal has depreciated the PayPal Standard API which requires the use of their IPN (Instant Payment Notification) system which has been awful for as along as I can remember (and often causes orders to not complete since the IPN never gets sent). I would enable the PayPal Express gateway in Store > Settings > Payments Methods then Add New Payment Method which should give something that looks like:
PayPal Express Checkout requires an API Username, Password, and Signature. These are different from your PayPal account details. You can obtain your API details by logging in to your PayPal account, and clicking Profile > My Selling Tools > API Access > Request/View API Credentials > Request API Signature.
Once you have enabled the gateway make it the default, if you have hardcoded the original Gateway Short Name in any of your templates you will need to change that to the paypal_express short name and then you can disable the PayPal Standard gateway.
PayPal Standard was removed in Store 1.6.0, for precisely this reason. It is extremely unreliable. I'm not even sure how you are still using it with Store 1.6.4.
It's definitely worth upgrading to the newer PayPal Express gateway which also ships with Store.
