How to add paid stamp into an invoice?

Adding a “ Paid” stamp is one of the premium features of Challan. In order to add a Paid Stamp into an invoice follow the steps below:

1. Go to the Woo Invoice > Settings from your WordPress Dashboard.
2. Click on the Invoice tab.
3. You will find a Paid Stamp sub-section. Toggle the Enable Paid Stamp.
4. There are a variety of Paid Stamps. Choose which fits right into your invoice.
5. You can customize the opacity of the stamp. For example: If you want the stamp opacity 50%, put 0.5 as the Paid Stamp Opacity value.

Custom paid stamp:

If you want to add a custom paid into the invoice, then use the below filter. 

add_action('woo_invoice_paid_stamp', 'woo_invoice_custom_paid_stamp',10,1);
function woo_invoice_custom_paid_stamp($paid_stamp_url) {
    return "paste your custom paid stamp url";
}