Hi,
1. You need to provide your merchant ID in the settings of the PayPal Checkout payment plugin:
www.hikashop.com/support/documentation/4...form.html#additional
With the merchant ID provided, the plugin will automatically check the situation of your PayPal account and display information about it on the options page once saved once.
It will probably tell you that you hit some kind of limit with your PayPal merchant account, and you need to do something with PayPal like provide legal documents so that your PayPal account can continue receiving credit card payments with the form.
www.paypal.com/in/brc/article/activate-your-business-account
The steps can be different from one country to another in order to comply with local rules. The information the plugin will display in the settings should help understand what needs to be done on your end.
2. The white popup is because you've activated the "System - HTTP Headers" plugin in the Joomla plugins manager, but you didn't set the "Cross-Origin-Opener-Policy" setting to "sam-origin-allow-popups", which results in the PayPal popup being blocked.
This is also mentioned in the PayPal Checkout payment plugin documentation page, so I recommend reviewing it once:
www.hikashop.com/support/documentation/4...out-form.html#issues