You can find the following error message there:

Object
123456:Array[1]
0:Object
code:"400007 - WRONG_SALE_PRICE_PERIOD"
title:"The start date for the reduced price must be today or later."
path:"/products"
jsonPath:"$.productVariations[?(@.sku==\"123456\")].pricing.sale.startDate"

This indicates that your start date in the variant 123456 is in the past.
However, it must necessarily be in the future, as due to technical reasons we have a time offset of about 2 hours (Background: Otto Market uses a different time zone than PlentyONE).

Therefore, adjust the start date of your variant so that it can be accepted by Otto.