Why do I get the error "The sender in the envelope 'xxxxxx@tradeplace.com' doesn't match the specified domain 'YYYYYY'" ?

This article will help you resolving the error : 'xxxxxx@tradeplace.com' doesn't match the specified domain 'YYYYYY'

In short, this error says you are not using the correct Tradeplace Identifier when sending your message.

When you have a Tradeplace direct connection account, you can see 2 parameters when going to Company/Business account

You can see you have a Domain and a TP-ID (Tradeplace Id). They are linked together.

Then if you go to 

Company/My transport definitions

You have the URL where to send your message. The domain is part of this URL.

So make sure you are using the Tradeplace Identifier that is matching the URL/Domain to where you are sending the message.