I’m the author of the Aelia plugin mentioned, I’ve been asked to look into this. Based on what we have seen on the site, that’s not an issue on our side. However, the root cause does seem to be the one described:
It would seem there is a disconnect between the currency provided when the JS script is loaded, and what’s being used server side when API requests are made
This is a slightly imprecise statement, but it’s in the right direction. In a multi-currency environment, the functions get_woocommerce_currency() and WC_Order::get_currency() may or may not return the same value. The former returns the active currency at a given time, which may change depending on the context, whereas WC_Order::get_currency() always returns the currency in which an order is placed. The two are not the same thing, and can’t be used interchangeably.
In the specific case reported by @henrybaum , the site is using multiple currencies, and it’s configured so that when a customer chooses a country at checkout, the currency in which the order is being placed changes as well. For example, a customers choosing US will see USD, a customer choosing UK will see GBP, and so on. Due to that, the following can happen:
- When the checkout page is loaded, the currency is USD. Calling
get_woocommerce_currency() returns USD.
- The customer changes the country to France. WooCommerce triggers a “refresh order” event, which is a fetch/Ajax call (i.e. it doesn’t refresh the page). The call passes the newly selected country (Spain) and that changes the currency to EUR.
- The customer places the order. The order is placed in EUR, as it should be.
The “disconnect” between the currency on page load and the one after the checkout refresh is not due to an error, it’s due how the system works. Quite simply, at the time of a “page load” event it’s not possible to determine with certainty in which currency an order will be placed. Fetching the currency at that time could lead to a discrepancy when the checkout is actually started.
Suggested solution
To address the issue during the payment process, the currency to be used for payments should only be fetched from the order when it’s placed. That value never changes (our Currency Switcher doesn’t even take part into the payment process, and never alter existing orders). If you need to build a URL for the PayPal SDK, then the currency should be stored into a variable and added to the URL as the second to last step, just before calling the PayPal service.
For the sake of clarity, this behaviour is nothing new. The currency selection has been working this way for at least a decade. The fix I described is something we recommended to other developers, and it should be sufficient to prevent the error.
