You will not be asked to pay for any additional charges from either the carrier delivering your Tonic products or from your government - all is included in the price that you pay for your products.
For your order to ship from the UK to EU countries without customs stops, companies need to be IOSS compliant. This means the company pays your import VAT on your behalf, meaning your package will simple be shipped and arrive at your door. You will not need to pay handling charged or VAT on the package*. Tonic are now IOSS compliant so your orders can be handled fiction free.
*This however only is applicable to orders under 150 EUROS. Orders over 150 Euros will have charges on entry.