The following simulation illustrates a Hosted Payment Process Result error during Pay Invoices by Email where a Braintree Connection is primary and a PayPal Connection is the fallback. 

Create a Pay Invoice by Email invitation selecting invoices where the Customer Reference is ERR03 and the open amount is >=$3000.

Receive the email and click Pay Now.  Select the invoice to pay and enter a payment amount equal to $3000.

Enter the credit card information and submit the payment to simulate the Payment Process Result error.   Notice the notification to Retry.

Click retry and the fallback payment form will be presented. Remember that since Paypal is the fallback in this scenario anything over $1000 will decline.  Therefore, this is the end of this simulation.