ADAPTER.HTTP_EXCEPTION - HTTP 500 Internal Server Error

Hi guys,

I am encountering an error when sending a message (XI 3.0 to SOAP 1.1) to the target web service. This is the error I am getting:

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The target web service does not send any acknowledgment message to PI as agreed. I've tried sending directly to their system via SoapUI and the message was received. Please advise. Thank you in advance!