Use API to reduce parts from a lot

[mulix]

I'm working on a simple frontend for Part-DB.
Unfortunately, I'm struggling to reduce parts from a lot.
The API documentation contains the endpoint /api/parts/{id}, which represents access to a part.

To decrease the part with ID 137, I use, for example, a
PATCH to /api/parts/137 with the JSON body
{ "partLots": [ { "@id": "/api/part_lots/122", "@type": "PartLot", "amount": 4, "id": 122 } ] }

Unfortunately, that doesn't work. The result is
{ "@id": "/api/errors/400", "@type": "hydra:Error", "title": "An error occurred", "detail": "Nested documents for attribute \"partLots\" are not allowed. Use IRIs instead.", "status": 400, "type": "/errors/400", "description": "Nested documents for attribute \"partLots\" are not allowed. Use IRIs instead.", "hydra:description": "Nested documents for attribute \"partLots\" are not allowed. Use IRIs instead.", "hydra:title": "An error occurred" }

So, how do I decrease or increase a part in a lot using the API?

Best regards,
Michael