Amazon: The caller account is not registered as a marketplace application to execute third party transactions

I'm working in Amazon FPS API integration, while requesting the API using "Pay" model with RecipientTokenId(I.e Merchant accept marketplace fee) , CallerReference, TransactionAmount and SenderTokenId. I'm receiving the following exception

Caught Exception: The caller account is not registered as a marketplace application to execute third party transactions. Response Status Code: BadRequestError Code: NotMarketplaceAppError Type: UnknownRequest ID: 96a2771e-85a0-4677-80dc-bf0740ed8893 XML: NotMarketplaceAppThe caller account is not registered as a marketplace application to execute third party transactions.96a2771e-85a0-4677-80dc-bf0740ed8893 FYI.. Simple Pay transaction is working fine that is, requesting the API without RecipientTokenId

Can you please provide me the link where I can register or do we have any settings to enable the third party transaction for Marketplace?

Thanks.