Why does Merchant Center say my Shopify products are missing shipping costs?

Short answer

Google has no shipping cost for the product, and it says these products won't show to customers until you add one. On Shopify the rates can be imported from your store through the Google & YouTube channel. Shopify says only rates in the General shipping profile sync, so custom shipping profiles and unsupported carrier rates are the first things to check.

What the issue means

Google's fix page says some of your products are missing shipping costs and that they won't show to customers until you add a shipping cost. Shopify's wording is that if your offers don't include shipping information, the offer is disapproved.

Google says shipping costs are required for Shopping ads and free listings in a list of countries that includes the United States, the United Kingdom, Canada, Australia, Germany and France, and that you may be required to provide them in more countries under local laws. The cost can come from the shipping settings of the account or from a shipping attribute on the product.

Why a Shopify store's rates may not reach Google

Shopify says only shipping rates in your General shipping profile can sync to Google Merchant Center.
Shopify says that if you use custom shipping profiles, rates sync incorrectly and cause errors.
The Google & YouTube channel supports carrier-calculated rates only for certain carriers and services in Australia, Germany and the United States.
With an unsupported carrier, or in another country or region, Shopify says you need custom flat shipping rates.

Where to look on Shopify

See which shipping setting the channel uses. In your Shopify admin go to Sales channels > Google & YouTube, click Overview > Settings, and in the Product feed section click Select beside Shipping settings. The two choices are Automatically import settings and Manually set up shipping settings in Google Merchant Center.
If the setting is automatic, check which shipping profile the flagged products are in. Rates outside the General shipping profile are not among the rates Shopify says can sync.
Check the rate type. If the rates are carrier-calculated and your carrier or country is not one the channel supports, add custom flat shipping rates.
If the store's rates can't be imported, set shipping in Merchant Center instead. Google's steps: go to Products & store, select Shipping and returns, and on the Shipping policies tab select Add shipping policy, then Shipping for online products.

Google's advice is to set up the account's shipping settings first and to use the shipping attribute only to override them for specific products.

After the fix

Google says the change may take 24 to 72 hours to show in your account and on the Needs attention page.

Questions

Does Google show a product with no shipping cost?

No. Google says these products won't show to customers until you add a shipping cost.

Can I use carrier-calculated rates?

Shopify says the Google & YouTube channel supports them for certain carriers and services in Australia, Germany and the United States. Otherwise you need custom flat shipping rates.