Generating Mailchimp API and Adding a List of Subscribers
Note: This manual is for osCommerce v4.
After you accessed your Mailchimp account click on Profile option.
Click on Extras drop down list and then on API key option.
Click on Create A Key button (by default there is none).
If there is not a single list of subscribers add one according to the following actions.
Admin > Marketing > Newsletter
Add key > Save
Select list > Save
Select store (it is added on the fly if there is none on Mailchimp) > Save
There is the link under the client’s email that needs to be sent.