White blank page after clicking on submit button

Hello everyone,
I'm using payment form on my website. There are two Radio buttons, "Online registration ($35) and At door ($40)"
I'm using value for fee as
35
0
If the user select "At door($40)" then the payment should be 0 , but when they click on "Submit" button at the confirmation page, the screen goes blank. In short, if i place 0 payment in my form, it shows blank page. Please help
website url

Hi

Maybe something wrong with the settings on your site causing the issue. Please submit a support ticket sending us super admin account of your site so that I can check to see what's wrong and get it sorted for you

Tuan

Hello Tuan,
Thank you for the quick response, i have just submitted the support ticket please check.

It is night time here now, so we are going to check it on tomorrow morning. Your ticket should be sorted in about 12 to 18 hours from now . Please wait for us.

Regards,

Tuan