How to Send Form Submissions to Brevo (Sendinblue) in 2026

Why route Brevo signups through your own form

Brevo (formerly Sendinblue) is a capable, EU-based email and marketing platform. Its hosted subscription forms work, but they're styled within Brevo's limits, load Brevo's script, and give you no independent spam filtering or submission record.

Own the HTML and route it through splitforms: you get a fully custom, fast form with an AI spam classifier, email notifications, and an auditable dashboard, while Brevo stays your email platform. A small proxy turns each signed webhook into a Brevo contact create/update with your list and attributes.

Step 1 — Get your Brevo API key and list ID

In Brevo, open Settings → SMTP & API → API Keys and create a key. Find the target list ID under Contacts → Lists (the numeric ID shown when you open the list). Store both as environment variables on your proxy host — never in the browser.

Step 2 — The splitforms → Brevo proxy

splitforms fires a signed webhook to your endpoint; the proxy holds the API key and creates/updates the contact. Cloudflare Worker version:

export default {
  async fetch(req, env) {
    if (req.method !== "POST") return new Response("Method Not Allowed", { status: 405 });

    // 1. (Recommended) verify the splitforms HMAC signature header here.

    const submission = await req.json();
    const f = submission.data ?? submission;
    if (!f.email) return new Response("no email", { status: 400 });

    // 2. Create or update the contact in Brevo
    const res = await fetch("https://api.brevo.com/v3/contacts", {
      method: "POST",
      headers: {
        "api-key": env.BREVO_API_KEY,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        email: f.email,
        attributes: {
          FIRSTNAME: (f.name ?? "").split(" ")[0],
          LASTNAME:  (f.name ?? "").split(" ").slice(1).join(" "),
          SMS: f.phone,
        },
        listIds: [Number(env.BREVO_LIST_ID)],
        updateEnabled: true, // upsert if the contact already exists
      }),
    });

    if (!res.ok && res.status !== 204) {
      return new Response(await res.text(), { status: 502 });
    }
    return new Response("ok", { status: 200 });
  },
};

updateEnabled: true makes this an upsert, so a repeat submitter updates rather than errors. Deploy the Worker and paste its URL into your form's webhook settings in the splitforms dashboard. Verify the webhook signature — see send form data to a webhook.

Step 3 — The form

Your public form only talks to splitforms with the public access key. Swap YOUR_ACCESS_KEY for the one from your free account.

<form action="https://splitforms.com/api/submit" method="POST">
  <input type="hidden" name="access_key" value="YOUR_ACCESS_KEY" />
  <input name="name" placeholder="Name" />
  <input name="email" type="email" required placeholder="Email" />
  <input name="phone" type="tel" placeholder="Phone (optional)" />

  <label><input type="checkbox" name="consent" required /> I agree to receive emails</label>

  <!-- honeypot -->
  <input type="checkbox" name="botcheck" style="display:none" tabindex="-1" autocomplete="off" />
  <button type="submit">Subscribe</button>
</form>

What to do next

• Other email tools: Kit (ConvertKit) · ActiveCampaign · Mailchimp
• Webhook fundamentals: send form data to a webhook
• Consent + privacy: GDPR-compliant submissions
• Ready to set it up: get a free access key

FAQ