I was having the same issue after purchasing my laptop from a third party. What worked for me was to input the company name and the postal code that was provided on my email order receipt.
I purchased a new U2419HX monitor from B&H. When I try to register it, I am presented with "This service tag holding product cannot be processed for retail registration. Please click here for transfer of ownership." Please advise.
Unable to register monitor (service tag can't be processed)