To let ProveSource capture sign-ups from your Brevo forms automatically, embed the form on your page with Brevo's HTML or Simple HTML code.
In Brevo, go to Marketing > Forms > Sign-up and open your form.
In the Share step, find the Embed section and select the HTML or Simple HTML tab. Brevo selects Iframe by default, so make sure you switch tabs.
Copy the code and paste it into your page.
Make sure the ProveSource code is installed on the same page as the form.
The Iframe option won't work, because ProveSource can't read forms inside an iframe.
More about Brevo's embed options: Create a sign-up form in Brevo.