cancel_url shortcode not working

You need to use the correct shortcode (that allows you to specify the “cancel_url”. The correct shortcode for you to use is the [wp_paypal_payment_box] one.

Please read the following documentation page (the section with the other shortcode with parameters) then use that to fully customize your PayPal payment box:
https://www.tipsandtricks-hq.com/wordpress-easy-paypal-payment-or-donation-accept-plugin-120

You also need to specify some of the other required parameters with that shortcode. Where your item and price parameters in the shortcode.

Remember this shortcode is a completely seperate shortcode that lets you craete the payment button via the shortcode parameter (it doesn’t have any association with the settings).

For example, the following would be a valid shortcode:

[wp_paypal_payment_box email=”your@paypal-email” options=”Red Shirt Payment:5.50|Black Shirt Payment:10.00|Other Payment:15.95″ cancel_url=”http://url_here/”%5D