Variable Price is an extension of the Checkout for PayPal plugin that can be used to add a price field to your PayPal smart payment buttons. This lets buyers set the amount they will pay for your products. It can also be used to accept PayPal donation payments.
In order to add a price field you can use the following shortcode.
[checkout_for_paypal item_description="My item description" amount=""]
Leaving the amount parameter empty implies that you wish to allow buyers to enter a custom amount for this item.
When the PayPal smart payment button is rendered on the front end, a price amount input field will appear with it.
If you wish to allow buyers to enter a custom description for this item, you can leave the item_description parameter empty.
[checkout_for_paypal item_description="" amount=""]
The default labels for the description and price amount input fields can be customized in the extension settings (Checkout for PayPal > Variable Price).