In order to connect your SendinBlue account to your Shopify store you need to create a SendinBlue account first (create account here).
Already using SendinBlue? Great! Continue step 2.

Step 1b) Create a Shopify account
No Shopify account yet? You can easily create an account here.

Visit the SendinBlue app in the Shopify app store here and click on the green GET button.

Your now forwarded to the install page. Click the blue button 'INSTALL APP'.

A) Export existing customers
​You may already have customers and subscribers and want to export them to SendinBlue. Use this step to export existing data.

CAUTION: existing customers in SendinBlue are going to be unsubscribed when they don't have the 'accept marketing' checkbox in Shopify. So make sure they are saved in a different SendinBlue list.

B) Configuration for Subscription submitted -> use our URL (only for non-sectioned themes)

The steps for this tutorial differ depending on whether you are using a sectioned or a non-sectioned theme. To figure out whether your theme supports sections, go to the theme's Edit HTML/CSS page. If there are files in the Sections directory, you are using a sectioned theme. Non-sectioned themes were released before October 2016, and do not have files in the Sections directory.

If you are using a sectioned theme, new contact who subscribed through your section signup form will automatically add to your Shopify customer section. If you are using non-sectioned theme, then you can use this URL as a custom Form Action URL in case your Shopify theme only supports Mailchimp integration (Non-sectioned theme).

You can paste this URL in Shopify in the Mailchimp form action URL field when editing your theme's footer.

C) Connect you SendinBlue account
Click the orange button to connect your SendinBlue account.

 
Enter your Sendinblue API key below. Go to your Sendinblue API key page https://my.sendinblue.com/advanced/apikey. 

Copy the Version 2.0 API key and paste it in the field below. Click ' Test and Save'.

You'll see a success message:

When the credentials are incorrect, we'll show this message:

D) Configure your list(s)
When you already use lists in SendinBlue you can select a mailing list for subscribers and customers. No lists yet? 

Just create one for subscribers and customers, refresh the dropdown list in this step and it will appear new in the dropdown list.

Please enter your email address so we can send you a message if problems occur with your integration. Then press the orange button 'FINISH INSTALL'.

We're now connecting your Shopify store to SendinBlue. When the installation has succeeded we're showing this message: