Log in to your Sendinblue account.
In the upper right menu, select "SMTP & API"
Select and copy your "v3" API key:
Log in to your Wisepops account.
Open or create a popup with a sign-up form.
Click on your sign-up form.
In the left menu, click on Sync, then on the Sendinblue icon:
Paste your API key and click "Submit"
In the "list" menu, choose which list you'd like new subscribers to join: