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Business Central API v2.0: purchase invoice line unitCost resets to 0 when locationId is set

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Posted on by CU21011339-0

Hi everyone,

I’m integrating with Dynamics 365 Business Central using the standard REST API v2.0.

**Issue:** When I create **purchase invoice lines** and include **locationId**, the line’s **unitCost** (Direct Unit Cost) ends up as **0** (or gets reset to 0), even though I send a non-zero value.

What I’m doing

1. Create Purchase Invoice header via API
2. Create Purchase Invoice line via API with a payload similar to:

json
{
"lineType": "Item",
"itemId": "<item-guid>",
"quantity": 1,
"locationId": "<location-guid>",
"unitCost": 12.34
}

Questions

1. Is it expected that setting `locationId` causes `unitCost` to be recalculated/overwritten on purchase invoice lines?

2. What’s the recommended approach to reliably set unit cost for item lines with a location (standard API only), or is a custom API/action required?

Any guidance or known limitations/bugs would be really appreciated.

Thanks!

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Dynamics 365 Business Central

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OussamaSabbouh 17,577 Super User 2026 Season 1 on at

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Hello,

This is expected with the standard BC v2.0 API—when you POST a purchase invoice line with itemId, quantity, and locationId, Business Central runs its normal validation logic (same as the UI) and recalculates Direct Unit Cost, which can overwrite the unitCost you send (often ending up as 0), especially since JSON field order isn’t guaranteed. The standard, supported workaround is to POST the line first with all “driver” fields (item, quantity, location, UoM), then PATCH the created line to set unitCost afterward; if even PATCH gets overridden, the only reliable solution is a custom API or custom action that controls the Validate() order and sets the cost last.

Regards,

Oussama Sabbouh

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Dhiren Nagar 2,890 Super User 2026 Season 1 on at

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Hi,

I have not tried this with my environment but here is a simple suggestion that if the unit cost is getting override, what you can do is first post the record with key fields. Then patch it with unit cost to update the value.

This will help updated only unit cost in next API call.

I hope this helps.

Regards,

Dhiren.

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