Trying to submit PATCH to existing FPVendPackingSlip entity

Hello,

I'm trying to submit a PATCH request to update a FPVendPackingSlip entity. The meta-data for this entity is as follows:

<EntityType Name="FP_VendPackingSlip">
<Key>
<PropertyRef Name="dataAreaId" />
<PropertyRef Name="PackingSlipId" />
<PropertyRef Name="ReceiptLineNum" />
<PropertyRef Name="DeliveryDate" />
</Key>

If I perform a get with the following, I find the entity just fine:

/data/FPVendPackingSlip?$filter=dataAreaId%20eq%20%27fpus%27%20and%20PackingSlipId%20eq%20%271%27%20and%20ReceiptLineNum%20eq%202%20and%20DeliveryDate%20eq%202021-04-28T12:00:00Z

But, when I try to PATCH the entity, I'm including the data elements in brackets as follows, in accordance with the key of the entity:

/data/FPVendPackingSlip(dataAreaId='fpus',PackingSlipId='1',ReceiptLineNum=2,DeliveryDate=2021-04-28T12:00:00Z)

When I try this, I always get "No route data was found for this request."

This is the same approach I take for updating other entities without any issues. Does anyone know how I need to change the OData parameters for the PATCH request to successfully find and update the entity?

Thank you!

Billy