There are few possible reasons that result in an error, such as : 

1. Connection time out.

2. Heavy website traffic which leads to slow loading. Please do not refresh the payment page.

3. You have refreshed the payment page or closed the payment browser while payment is in process.

Kindly check your email inbox, spam or junk folder 5 minutes after payment. If there is no email received, please click here and choose either "Forgot Student ID" or "Forgot password" to retrieve your login credentials.