This wasn't an issue until today, no other website or code changes were made in the last week. My only guess is that intuit changed their API response handling.

Within the PaymentClient class the "charge" method has a duplicate httpClient->send method call. This is now causing the first call to have a valid "$response->getBody()" value, while the second call, which is the one that gets returned by the "charge" method to have an empty body value. Up until today the second "send" method call returned a valid body response. Today's issue caused the credit card to be charged successfully, but the order to fail because the body was empty and the response couldn't be verified as successful or not. Commenting out line 95 resolves the issue.

Line 95: $response = $this->httpClient->send($request);

Another item to note, there is also a duplicate "send" method call on line 110 within the voidChargeTransaction method of this same class.