With the error, it looks like you are trying the inbound flow (partner sending to Oracle B2B) and it is failing to identify the incoming document.
Couple of Points :
- If you are using the custom document, then please check the Xpath expression and xpath value. It has to match with the incoming payload
- If you are using AS2 connectivity, please check the AS2-id in the configuration and ensure the same is configured with partner.
Please elaborate your flow for better help