The message can look as follows:

Object
response:Object
status:"error"
code:422
message:"Client error: `POST https://live.api.otto.market/v2/quantities` resulted in a `422 Unprocessable Entity` response:
{"errors":[{"path":"/v2/quantities","title":"Error while processing request: 3726","code":422,"detail":"Error: SKU is un (truncated...)

The code 422 indicates that OTTO does not recognise the SKU. As a result of a new creation, it may be that we have already created a SKU for OTTO, but it is not yet listed there at all.
Only when the product data of the variant is correctly transmitted to OTTO can the stock be reconciled using the SKU.