Mailchimp and Shopify are consciously uncoupling.
Quick Primer: Mailchimp is an Email Service Provider (ESP, for short) who integrated rather smoothly into Shopify. When the two systems played nicely with one another, it was a marriage made in heaven. With relative ease, you could develop a full email marketing campaign without leaving the platform.
That’s no longer the case, and it’s a messy breakup. Shopify says “Mailchimp refuses to synchronize customer information captured on merchants’ online stores and email opt-out preferences. As a result, our partner ecosystem can’t reliably serve their customers or comply with privacy legislation.”
Mailchimp says “we asked Shopify to remove the Mailchimp for Shopify integration from their marketplace, because Shopify released updated terms that would negatively impact our business and put our users at risk.”
The end result of this, is that if A) your website is built on Shopify and B) you use mailchimp then C) you need to make changes, and fast.
Realistically, there are two ways to make these changes. First, you can use a third party tool like Zapier to connect the two systems. Second, you could switch to another ESP, preferably Klaviyo.