Can not check new App preview

Hello,

I am new to cloulflare. I just finished setting up for on of my domain.
I was checking the Apps section. When I tried previewing one of listed apps I wasn’t able to preview it. It gave an error “An error occured loading this page. Please double check the URL. If it continues to fail, please try again later or contact for assistance”, I don’t know what to do next.

Please help me with this as It would be pretty useful if I am able to preview App before deploying it.

Thanks in advance for help