Symptom: Either your popup (Form) is showing but the conversion rate is lower than expected, or visitors are filling out the popup but their email or phone number isn't appearing in your subscriber list.

TL;DR. "List not growing" usually breaks into two distinct cases:

Case A: popup is showing but conversion is low (weak offer, wrong audience, wrong moment, broken funnel).
Case B: visitor submitted but isn't in your list (DOI not confirmed, wrong list mapped, analytics lag).

Pick the case that matches your symptom.

Case A: Popup conversion is low

The popup is being shown to visitors, but few are subscribing.

First, define "low"

Before debugging, set a baseline:

Below 2% conversion: definitely a problem.
2 to 5%: there's room.
5 to 8%: typical; small wins available.
8%+: you're doing well, focus on revenue per conversion instead.

A1. Is the offer compelling enough?

A 5% off popup will under-perform a 15% off popup almost every time, on the same traffic.

Try:

10% off vs 15% off vs free shipping vs $20 off (for orders over $100).
A bundle offer vs a simple percent off.

If your offer is the same as your competitor's, you're not standing out.

A2. Is the audience right?

Open the Targeting dialog. Common mismatches:

Showing on all pages: visitors on a blog post you wrote 3 years ago aren't your buying audience. Restrict to product / collection pages.
All countries: your offer might not apply to international visitors. Restrict to countries where you ship.
Returning visitors only: returning visitors saw the popup last time and didn't subscribe; they're a tougher audience than New.

Fix:

Page targeting: product or collection pages only.
Country: where you actually sell.
Visitor type: New visitors (default), reset if you changed it.

A3. Are the triggers right?

If the popup fires too early, visitors haven't formed intent yet. Too late, they've left.

Wait time = 0 seconds: most visitors haven't even read the headline. Try 5 to 10 seconds.
Wait time = 30 seconds: half your traffic is gone by then. Try 5 to 10 seconds.
Scroll depth only: visitors who don't scroll never see the popup. Layer wait time + scroll with OR.
Exit intent only: catches only people about to leave. Layer it with wait time + OR.

A good default:

Wait time = 5s (desktop) / 3s (mobile), OR
Scroll depth = 30%, OR
Exit intent.

Visitors hit the popup at the first of those three.

A4. Is the funnel leaking?

In analytics, look at the step funnel (see Read your popup analytics):

Below 70% on the Teaser to Open transition: the teaser copy isn't enticing.
Below 60% on the first step to second step: either the first step is heavy, or the connection between value (the offer) and ask (your info) isn't clear.
Below 30% on the SMS step: SMS adds friction. This is usually fine; it's a heavier ask. Don't expect parity with email.
Below 50% on Web Push: visitors saw the native "Allow notifications?" prompt without context and tapped Block. Add a Micro Commitment step right before Web Push that explains what they'll receive (for example, "Get instant updates on restocks and flash sales").

A5. Is there a creative problem?

Open your popup in Preview mode on a real phone, not just desktop. Common creative issues:

Hero image is too large, pushing the form below the fold.
CTA button color doesn't contrast with the background.
Copy is too long; visitors scan, they don't read.
The discount value isn't in the headline: bury "15% off" inside three paragraphs and they'll miss it.

Case B: Visitor submitted but isn't in my list

The popup recorded a submission but the contact isn't showing in your email or SMS list.

B1. Email: is DOI on?

If Double opt-in is enabled on your Email step (see Email DOI and SMS / TCPA consent compliance):

Subscribers only appear in the list after they click the confirmation link in their email.
Expect 60 to 80% of submitters to confirm. The rest are in a "pending" state.

To check:

In your email service (Brevo or similar), find the contact by email.
If the status is pending or not confirmed, they haven't clicked yet.
Resend the confirmation email or remind the visitor to check their spam folder.

To turn off DOI (and accept all submissions immediately):

Open the popup in the editor.
Click the Email step.
Toggle Double opt-in off.
Save and Publish.

(Heads up: turning off DOI affects compliance. See Email DOI and SMS / TCPA consent compliance.)

B2. SMS: was the TCPA checkbox ticked?

The SMS step has a required TCPA consent checkbox. If the visitor submits without ticking it, the form blocks submission. But if you customized the SMS step and removed the validation, unchecked submissions could still register without consent. Audit the SMS step settings:

Open the popup, then the SMS step.
Confirm the consent checkbox is set to required.
Re-publish if you changed anything.

B3. Is the popup mapped to the right list?

Each popup is assigned a target list. If the assignment is wrong, subscribers do get added, just to a list you weren't checking.

To check:

Forms > Campaigns.
On the campaign card, click Subscriber lists.
See which email / SMS / web push lists are assigned.

If the list is wrong, change it and the next subscribers go to the right place. (Existing wrong-list subscribers don't auto-migrate.)

B4. Is there an analytics lag?

Subscribers usually appear in your list within seconds, but during peak traffic this can lag by up to 5 minutes. Confirm by waiting 10 minutes and refreshing.

If they're still missing after 10 minutes, it's not lag.

B5. Are submissions being blocked?

Check the popup analytics (see Read your popup analytics):

Impressions above 0: popup is showing.
Conversions equals 0: no one is completing the form.

If you have impressions but no conversions for hours on a high-traffic store, something is breaking submission. Check the browser console on your storefront for errors.

B6. Did you test in incognito with a real email?

Submissions go through normally in incognito, but if you used test@example.com, Brevo may reject or quarantine the contact. Use a real email when testing.