Problem:

I have generated an invoice for an order in Linnworks, however it is not displaying any Tax/VAT.

Reason:

It is important to distinguish if the Tax/VAT field is missing from the invoice entirely or if the field is present but is displaying the value of "0.00". Invoices that are generated in Linnworks pull flat, already-calculated data straight from the order record. The Template Designer doesn't run its own tax logic at the point of printing. It will simply display the same amount that is on the order. If you're seeing the value of "0.00" in the Tax/VAT field, it means that the Tax/VAT is 0 on the order as well.

Solution:

Depending on the source of origin, Linnworks will apply different Tax settings to the order. For orders created in Linnworks either directly or with an import, the system will apply either the Item Tax Rate or the Delivery Country Tax Rate.
Majority of our channel integration offer the possibility to use a setting called "Use Channel Tax". This means that for channel orders, the Tax rate applied to the order will be whatever value is sent to Linnworks with the order data from the sales channel. If such setting is not enabled, Linnworks will use the aformention methods to apply Tax/VAT to the order.

If the value is "0.00" instead of an expected Tax Rate, first try to trace down how the Tax should be applied to the order.

If the order is a Direct order (or imported):

Check the order SKU under Inventory > My Inventory > [SKU] > General and confirm whether an Item Tax Rate has been set and "Country Specific Rate" disabled. If so, Linnworks should be applying the item-level Tax Rate. If "Country Specific Rate" is enabled, Linnworks will apply Country-specific Tax Rate to the order. It is stored under Settings > General Settings  > Countries. If neither the item nor the country has a rate configured, Linnworks has nothing to apply and the order will correctly calculate the rate at 0%.

If the order is a Channel order:

Check the channel's integration settings and confirm whether "Use Channel Tax" is enabled. If it is enabled, Linnworks is not calculating the Tax itself - it is only displaying whatever value the channel sent through on the order. To see this raw data, check the Order XML and look for the tax values the channel actually passed in. If the channel sent the order through with 0 Tax then 0.00 is the correct value.

If "Use Channel Tax" is disabled, the order will instead follow the same Item Tax Rate / Delivery Country Tax Rate logic as a Direct order described above.