Not loaded form properly on sandbox mode

[ghost]

form not loading properly on sandbox mode.
https://www.screencast.com/t/wYQWRwFHgI
It shows the first-time iframe, once I click on place order button it loaded form, also when i put correct test card data at the first time it shows error message "invalid card number" and same card number when I tried with second time and then place an order. it working.

I wanted to work properly. but it not working on sandbox mode so i can not try with production mode until it not work with sandbox.

can you suggest?