Custom Purchase Button

Hello there,

I wish make my purchase button like this – https://codepen.io/devigor/pen/qrdKXd

So, that as the payment is processed, it shows loading, and then redirects.

Can you please help, how can I make it run only when all the required fields are filled.
As showing this processing won’t be good when the after clicking purchase button it says fields required error.

Can you help with this,please