To restrict MerchMixer Products only to your US based customers, you will need to make some changes to your Shopify admin.
You can view more details from the Shopify Community on how to restrict products here
- In your Shopify admin, go to Settings > Shipping.
- In Shipping profiles, click Create new profile.
- Enter a name for the profile.
- In the Products section, use the search bar to add products to the shipping profile.
- Address any changes you need to make to your locations. Refer to Manage your locations for more information.
- For each shipping zone that you want in your shipping profile, complete the following steps:In Shipping to, click Create shipping zone.Name the shipping zone.Select the countries or regions that are part of the zone, and then click Done.For each shipping rate you want in the zone, click Add rate, choose the rate's details, and then click Done.
- Click Save.