You can find the following error message there:

Object
1234:Array[1]
0:Object
code:"100008 - INVALID_VALUE" 
title:"TESTMARKE is not a valid brand. Please enter a valid value. Please only select brands that you can query via the Brands endpoint in the API."
path:"/products"
jsonPath:"$.productVariations[?(@.sku==\"1234\")].productDescription.brand"
Trigger:"cli: artisan otto:item:report:result"

Due to the change of the product API to v3 from Otto Market, there have been adjustments regarding brands, among other things. These are no longer transmitted as names, but as so-called BRAND_ID.

Therefore, when using Custom Values, it must be ensured that the value stored there exactly matches the Brand ID, otherwise no transmission will take place.

Check your mapping in the catalogue under Brand and change the Custom Value to the Brand ID.