Dear HubSpot Support Team,
We are facing an issue with the Mobile Number property on the Contact object.
We have configured the Mobile Number property as a unique value field in HubSpot. However, when contacts are created through a form submission, HubSpot is still creating duplicate contact records with the same mobile number initially. After the duplicate record is created, HubSpot then shows the error stating that the mobile number is not unique.
This is a real estate B2C business use case, where customers often do not provide a reliable or unique email address during inquiry submission. Because of this, we cannot use email address as the primary unique identifier for form deduplication, and instead need HubSpot to properly handle deduplication based on mobile number, which is the most reliable identifier in our process.
Expected behavior:
- If a contact already exists with the same mobile number, HubSpot should update the existing contact (or prevent duplicate creation), rather than creating a duplicate record first.
Current behavior:
- Form submission creates a duplicate contact record.
- After creation, HubSpot displays an error that the mobile number is not unique.
Could you please investigate why the unique property validation is not preventing duplicate record creation during form submission and advise on the correct resolution for this use case?
Please let us know if you need any additional details from our side
Hi @Alekya
Thanks for providing such a detailed explanation.
From what you’ve described, the unexpected part is that the duplicate contact is created before the unique property validation is enforced. If the Mobile Number property is configured as unique, I’d also expect that constraint to be applied consistently during record creation.
I haven’t personally tested this scenario with form submissions using a unique Mobile Number property, so I can’t confirm whether this is expected behavior or a limitation of form deduplication.
A couple of questions that may help narrow it down:
- Are these HubSpot forms, or are the submissions coming through an API or third-party integration?
- Is the duplicate created every time, or only under certain conditions?
If this is happening with native HubSpot forms, it would be helpful for a HubSpot moderator or product specialist to confirm whether unique property validation is expected to prevent duplicate creation during form submissions, or whether email remains the primary deduplication key in this scenario.
Hi @Alekya,
This is actually documented, not a bug HubSpot’s own docs confirm unique value properties aren’t supported in form deduplication, forms only dedupe by email, company domain, or record ID. Unique property validation only kicks in for manual entry and imports, which is why it works there but fails silently on form submissions before throwing the not unique error after creation. Since your use case has unreliable email but reliable mobile numbers, the workaround most teams use: let the form submission go through as-is, then run a workflow immediately after creation that checks for existing contacts with a matching mobile number, and merge or update if found. There’s no native form-level fix for this, it has to be handled post creation via automation.
@Alekya
@TeeTech is correct, I’ve run into this too. We rely on phone number as a more reliable unique ID for 90% of the database, and had to jump through hoops to get here.
I built a lengthy, but useful workaround in 2024 that leans on Data Hub Deduplication rules. Still holding up, though I agree there should be an easier approach here. It’s a long walk to get here
Do you have Data Hub? Happy to share more resources on the solution I built, if so.
Debrief below.
Currently Not Supported by Hubspot: (Solved with workaround below)
1.) Marking default Phone Number fields as ‘unique,’
2.) Allowing/requiring unique fields in forms
3.) Syncing or copying Phone Number fields directly to a ‘Unique’ field in workflows or property syncs.
_____
Workarounds I’ve Built: (Data Hub Required)
1.) Rules:
- Require phone number in all forms or sources of incoming data. This field can’t be unique, but you can send the data to a unique field.
- Ensure that duplicate phone fields like Mobile Phone Number have been audited and consolidated into the Phone Number Fields
2.) Create two custom fields. (reference limit #3 above.)
-
Plain Text Phone Number, single line text. Strips phone down to standardized formatting and prevents legacy phone numbers with inconsistent formatting (frm pre-2025 updates) duplicates from sneaking through
-
Unique ID Phone Number. Purely operational for flagging duplicates. Not included in forms. Receives the formatted Phone Number and is used for de-duplication.
-
Plain Text Phone Number: Copy phone number here and use data hub to strip out and standardize formatting. Then, send the outcome string to a ‘unique ID property’
How to Use this Data:
- Create a duplicate alert rule for contact.Plain_text_phone_number.
2.) Logic for standard duplication review.
If contact: [Phone Number] or contact: [Mobile Phone Number] are known on a record and [Unique ID: Phone Number] is blank,
A contact record in the portal already has this number in use.
AND
the records should be reviewed for Duplicates.
Hi @Alekya,
This is - sadly - expected behavior. Deduplicate records in HubSpot
The following behavior is expected for unique value properties:
- Not supported in forms. If your goal is to update or associate existing records via form submissions, it’s recommended to use the default deduplication properties instead (i.e. Email, Company domain name, Record ID).
There is, as far as I know, no default way in HubSpot to make it behave differently. This functionality simply has not been developed yet.
Generally, this seems to be on the roadmap, see here: Phase 1 of 2 for CRM Property Validation on Forms
You could also submit a request to the product team here: https://community.hubspot.com/c/hubspot-ideas/59
As far as workarounds go, I would leverage Koalify, a third-party integration built for HubSpot, here. (Disclaimer: the link is an affiliate link which makes me eligible for commission). You can install the app through the HubSpot app marketplace or through my affiliate link. The steps are identical.
In Koalify, you could specify that contacts should be flagged as duplicates if they have matching phone numbers. You could then enroll the contacts into a workflow and use the Koalify “Merge Duplicate Record” workflow action to simply merge them.
Yes, you’ll briefly have duplicates after form submission, but the moment the duplicate is found (based on the phone number) it simply would be merged as per HubSpot merge rules, meaning that the latest value of the winner will be kept (winner to be defined by your primary duplicate rules in Koalify settings) and all activities of both records will be visible on the winning record.
Best regards
