3285201 - API upsert error "keyString cannot be blank"

When you use OData API to upsert data, it returns error "keyString cannot be blank".

You check the payload but cannot find any fields left blank.

"Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental." 

SAP SuccessFactors HCM

• OData API

This error means the request has a blank key for the entity.

It usually happens when you add parenthesis appending the entity, but didn't specify the key in the parenthesis.

Please remove the parenthesis in the payload. Or instead specify the correct key in the parenthesis.

OData API, business key, entity, payload, parenthesis  , KBA , LOD-SF-INT-ODATA , OData API Framework , Problem