If you are using the Google Channel, make sure to first disable automatic shipping, to avoid Shopify overwriting your Google Merchant Center settings.
Then in Google Merchant Center add your shipping rates using the same currency as you have submitted in the data feed. If you are using the free shopping channel app, that would be only 1 currency, not multiple as you indicated. The Google Channel app does not support multiple currencies which may be your issue.
And reprocess the feed. If you are using content API you can reprocess using the steps here: https://feedarmy.com/kb/how-to-reprocess-content-api-in-google-merchant-center/
If you want to use a data feed app that supports multiple currencies, then I recommend: https://apps.shopify.com/multiple-google-shopping-feeds