If you need to add social security withholding to your invoice, first you need to activate the option to do so. Click on your name in the top right, and on "Settings" in the dropdown list as shown below.

In the menu, select "Invoicing" under your company's name.

You will now find yourself in the invoicing options page. Toggle the first option, "Tax withholding" until it turns blue to activate it.

Once activated, go to the invoice template. Scroll down the form and click on the blue statement "Apply tax withholding".

Next, in the pop-up that appears, activate the second option "Social security withholding".

Next, you need to select the social security withholding type from the dropdown list. You can also select the reason for withholding and choose if you want to personalise the percentage of the withholding.

Once all the parameters are set, click on "Apply". The social security withholding will be automatically added to your invoice and will be calculated in the total taxable.

Great! Now your invoice is ready to be sent!