If you are seeing this error, you changed your store currency in the Shopify settings, but your Market (the region where you accept sales in Shopify) does not have a consistent currency as your store currency.
To fix:
Go to your store's settings in Shopify and select the currency you want to support.
2. Then still within your stores settings in Shopify, search for markets. For each market here you must set the currency to your store's currency