Feed Rejected - InvalidMarketplace
This is an error from Amazon because either your Amazon account is brand new or your Amazon account has become inactive for some reason.
To resolve this issue, please login to your Amazon Seller Central and re-submit your credit card/ banking financial details.
We've observed that this error usually goes away within 2-3 days after re-submitting your financial details on Amazon Seller Central [since it re-activates your account].
If you've just recently opened an Amazon Professional Seller Account, then you'll have to wait for about 2-3 days in order for Amazon to completely setup your account.
If problem still persists:
If you're still experiencing the same error, after waiting for 2-3 days, then please create a case with Amazon Seller Central so that they can assist you further.