The received sync MDN seems not to be in right format.

I am trying to send test data and I keep getting the below error. But I am not sure where to correct this.

The received sync MDN seems not to be in right format. As MDN structure problems are uncommon it might be that this is no answer of the AS2 system you wanted to address but perhaps a proxy or a standard web site? The following HTTP header values are missing: ["AS2-TO", "AS2-FROM"].

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AS2