Magento Open Source V2.2.3 Checkout error

[WZ_OZES]

I ran into an error when checking out from my Magento store. I set up a test account and checked out via the shopping cart (Proceed to Checkout). On the checkout page, everything is showing correctly. Shipping cost is set to Flat rate. Shipping address also appears to be ok. When I clicked Next, an error message came up saying "unable to save shipping information. Please check input data"

I went through the menu but found nothing. Is this related to an incorrect setting or something else?

[WZ_OZES · Accepted solution]

I solved the problem. I went to check the Magento Exception Log and found it was because of the exchange rate. Then I found the allowed currency has nothing selected which caused this error. After I selected allowed currency, the problem goes away.