Value UnexpectedValue for parameter PerUnitDeclaredValue is invalid Documentation

If Amazon returns an error message that creates an Order Note and/or email notification similar to:
Failed to submit order to FBA (click for full log). Error Message: Value UnexpectedValue for parameter PerUnitDeclaredValue is invalid. Reason: 1 error: The field Per Unit Declared Value has a value of EUR, was expecting GBP

This means that the currency type for the order from your store sent to FBA did not match your Seller Central account’s home region currency. The challenge with FBA and multiple currencies is that Amazon Fulfillment only allows one currency to be submitted with order data, and it must match the currency of your Seller Central account’s home region.

By default the plugin passes WooCommerce’s configured currency through to Amazon, which works fine for most sites. However, if you’re using another plugin to handle multiple currencies, FBA responds with an error like the one above. This scenario and others similar to it are exactly why the manual currency override feature/setting exists.

If your account’s home currency is GBP, set this for GBP in the Override Currency setting under WooCommerce > Amazon Fulfillment, and enter the best “middle road” conversion factor to use. Default value is 1. This is used in the “declared value” field that FBA requires. The only other option is to ensure that WooCommerce is configured to only handle payments in a single currency that matches your home region’s primary currency.

In any case, WooCommerce must always send the currency that Amazon expects because this is what your FBA account is based on. The error tells you how the currency field should be set, as it say: “…was expecting GBP.” In this case, you need to use GBP for that setting.