If you are shipping internationally with Hermes, Shiptheory passes not only the shipment/order value to Hermes but also the unit price of the products being shipped. This is a requirement from Hermes.
Hermes will reject the the label request if the total shipment value does not match the combined product values. For example, if your shipment total value has been manually set to £10, but you have two products on the order worth £6 each, totalling £12, Hermes will reject the request on the grounds that the values do not tally.
To prevent such rejections, Shiptheory will determine the total shipment value from the products for international Hermes shipments, rather than the shipment total value.
If you have any questions around this, please reach out to support.