HubSpot Domain Settings

When you embed a HubSpot form on a Flint landing page, HubSpot needs to know that your domain is an authorised source for submissions. If your domain is not listed in HubSpot's allowed domains, submissions may be:

• •Silently dropped or marked as spam
• •Blocked by HubSpot's bot-filtering rules
• •Missing from your CRM contacts entirely

This applies to two common scenarios:

• •Your custom domain is set up (subdomain or subpath) — you need to add that domain to HubSpot once
• •You have not yet configured a custom domain — your pages are served from a Vercel preview URL (e.g., your-site.vercel.app) and that URL needs to be added while you are still in that stage

This guide covers both cases.

HubSpot forms use a same-origin trust model. When a form is submitted, HubSpot checks the page's origin against a list of domains you have verified in your account settings.

Flint pages are not served from a HubSpot-hosted URL, so HubSpot has no prior knowledge of the domain. This is true whether your pages are on:

• •A custom subdomain you have configured (e.g., pages.yourdomain.com)
• •A subpath on your root domain (e.g., yourdomain.com/lp)
• •A Vercel preview URL — the default before a custom domain is set up (e.g., your-site.vercel.app)

In all three cases, HubSpot treats the origin as unknown and may flag or drop submissions. The fix is the same: add the domain to your allowed list in HubSpot.

• •A HubSpot account with Super Admin permissions (required to edit domain settings)
• •Your Flint landing page domain — this is the domain or subdomain where your Flint pages are live (e.g., pages.yourdomain.com or yourdomain.com)
• •At least one HubSpot form already embedded on a Flint page

If you have not yet set up a custom subdomain or subpath with Flint, your pages are served from a Vercel preview URL. This URL looks like:

your-site-name.vercel.app

You can find the exact URL by opening any of your published Flint pages and copying the domain from the browser address bar.

Add the Vercel preview URL to HubSpot

Follow the same steps below (Steps 1-4), but enter your Vercel URL as the domain (e.g., your-site-name.vercel.app).

Because Vercel controls the vercel.app DNS zone, you cannot add a DNS TXT verification record to it yourself. HubSpot may skip verification for external domains that do not support DNS access, or it may offer an alternative verification method — follow the prompts HubSpot displays.

Important: The Vercel preview URL is a temporary address. Once you configure a custom domain in Flint, your pages will move to that domain and you will need to add the new domain to HubSpot as well. Treat the Vercel URL entry as a short-term measure to unblock testing during setup.

1. 1.Log in to your HubSpot account
2. 2.Click the Settings icon (gear icon) in the top navigation bar
3. 3.In the left sidebar, go to Content > Domains & URLs
4. 4.Select the Domains tab

You will see a list of domains already connected to your HubSpot account (typically your main website and any HubSpot-hosted pages).

On the Domains page, click Connect a domain (or Add domain depending on your HubSpot version).

HubSpot will ask what type of domain you want to connect. Select External domain (also labelled "A domain I host elsewhere" in some versions).

Enter your Flint domain:

• •Subdomain setup: enter the subdomain (e.g., pages.yourdomain.com)
• •Subpath setup: enter the root domain (e.g., yourdomain.com)
• •No custom domain yet: enter your Vercel preview URL (e.g., your-site-name.vercel.app)

Click Next or Connect.

Note: HubSpot may attempt to verify domain ownership via a DNS TXT record. For custom domains, follow HubSpot's on-screen instructions to add the record at your DNS provider — this is separate from your Flint DNS setup and does not affect how pages are served. For Vercel preview URLs, you do not control the DNS zone, so HubSpot may offer an alternative verification path or skip this step.

After adding the DNS verification record, return to HubSpot's domain settings and click Verify.

Verification typically completes within a few minutes but can take up to an hour depending on DNS propagation.

Once verified, the domain will appear in your HubSpot domain list with a green Verified status. HubSpot will now accept form submissions originating from pages on that domain.

After verification, test that submissions are coming through correctly:

1. 1.Visit one of your Flint pages that contains a HubSpot form
2. 2.Fill in the form with a test email address and submit
3. 3.In HubSpot, go to CRM > Contacts and search for the test email
4. 4.Confirm the contact was created and the form submission appears in their activity timeline

If the contact does not appear, check the Forms > Submissions view in HubSpot for any flagged or filtered entries. Also confirm that the domain shown in the browser URL bar exactly matches the domain you verified in Step 2.

If your Flint pages are served under a subpath (e.g., yourdomain.com/lp), you need to add the root domain (yourdomain.com) to HubSpot — not the subpath.

HubSpot matches on the hostname only, not the path. Adding yourdomain.com will cover all pages at yourdomain.com/lp/* and yourdomain.com/*.

If your root domain is already listed in HubSpot (for example, because your main website is connected), your Flint subpath submissions should already be trusted. Check the verification status of the existing domain entry before adding a duplicate.

Submissions still not appearing after verification

• •Confirm the domain in HubSpot matches the domain shown in the browser address bar exactly (including subdomain prefix if applicable)
• •Check whether your HubSpot portal has bot filtering enabled. Go to Settings > Marketing > Forms > Spam submissions and temporarily disable filtering to rule it out
• •Confirm the form embed code on your Flint page uses the correct Portal ID and Form ID

Submissions stopped working after setting up a custom domain

If you previously added a Vercel preview URL (e.g., your-site-name.vercel.app) and have since configured a custom domain, your pages now serve from the new domain. Add the new custom domain to HubSpot using the steps above — the Vercel URL entry no longer covers submissions from the new address.

HubSpot says the domain is already connected

This means the domain (or its root) is already registered in your HubSpot account. In this case, no action is needed — submissions from that domain should already be accepted. If they are still not appearing, check the spam/bot filtering settings instead.

Verification record not detected

DNS changes can take up to 24 hours to propagate. If verification fails after an hour, double-check that the TXT record was added to the correct DNS zone and with the exact value provided by HubSpot. For Vercel preview URLs, DNS verification is not possible — if HubSpot is stuck on this step, try the alternative verification method or contact HubSpot support.