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Create a Contact linked to Customer from API

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Posted on by CU21111315-0

Hello,

I try to create a Contact (with type Person) record which is related to Customer record.

Tried several ways, but none seem to work (I was able to create Customers and unlinked Contacts). As I understood you do not link that Contact directly to Customer but to another Contact (with Type Company) which is automatically created when Customer is created.

I tried to create a new Contact (with type Person) with a link to Contact that automatically created Contact (with Type Company). I used this body:

{
  "displayName": "Test Contact",
  "phoneNumber": "555577777",
  "email": "test@test.com",
  "type": "Person",
  "companyNumber": "CU17414"
}
 


This request gives me such error: You cannot change Company No. because one or more unlogged segments are assigned to the contact.



Any ideas what this error means or how to properly link my new Contact?

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Dynamics 365 Business Central

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OussamaSabbouh 12,808 Super User 2026 Season 1 on at

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Hello,

You're using the Customer No. in companyNumber, but the API expects the Company Contact No. (the contact automatically created for the customer).

Fetch it from:

GET /customers({id})/contactsInformation → use contactNumber from the response → send that in companyNumber.

Regards,

Oussama Sabbouh

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Gregory Mavrogeorgis 992 Super User 2026 Season 1 on at

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Hi,

When you create a Customer in Business Central, the system also creates a Contact of type Company in the background.
But the important thing is:
That Contact has its own Contact No., which is different from the Customer No.
So when you tried this:

you were actually passing the Customer No., not the Company Contact No.
BC doesn’t allow that, and that’s what causes the “unlogged segments” error. It basically means “you’re trying to use a value in Company No. that I cannot use as a Contact.”

The correct way to do it

First, find the Company Contact that BC created for your customer.
You can get this by querying:

Contacts where type = Company, or

Contact Business Relations for your customer.

That record will have a Contact No. like CT000123.

Use that number in your request:

After that, BC will happily create the contact and link it under the company.

BC doesn’t let you link a Person Contact directly to a Customer.
Instead, everything goes through the Company Contact that represents the Customer.
So your job is simply to find that contact and use its number.

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Jainam M. Kothari 15,732 Super User 2026 Season 1 on at

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Hello,

You cannot directly set companyNumber when creating a Person-type Contact because Business Central manages company relationships internally.

The correct approach is to first create the Person Contact without linking it, then use the Contact Business Relation to associate it with the Company-type Contact that was automatically created for the Customer.

This error occurs because the system prevents manual changes to Company No. when relationship segments exist, so linking must be done through the proper relationship table or API endpoint rather than in the initial Contact creation request.

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