My subscription products can't be added to the cart on other markets when using Shopify's Managed Markets solution

There is a specific limitation with Managed Markets in Shopify, where the subscriptions currently only work in domestic markets. You can see this limitation listed by Shopify here: https://help.shopify.com/en/manual/international/managed-markets/requirements-and-considerations#considerations 

This doesn't mean that subscriptions in Shopify don't work with Shopify Markets functionality. This limitation is posed by Shopify only for the “Managed Markets” functionality.