Within the DigiFabster back office in the Payment & Taxes section, you can set up the Sales Tax/VAT/GST/MwSt/TVA which is valid in your country of residence.
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It will add the input taxes to any goods and services on the invoice, and by default, it will also add taxes to shipping costs you specify. 

It turns out that PayPal has exactly the same option, which can be added to the payment button: 

Now what happens is that first DigiFabster and then Paypal will add a tax amount, which will likely "amaze and disappoint" your end user.
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Our advice: Depending on which documents you use for your book-keeping, enable either the DigiFabster VAT feature, or the PayPal VAT feature, but don't use both.

Here is how to turn off tax on the Paypal site