AS signature failure for interop content type
In System Administration > Common Attributes page of the Console, the
excludedContentTypesForCanonicalization property is made editable.
While performing AS2 transactions, this attribute has all the content types that are
excluded from canonicalization.
To resolve the issue, add application/pkcs7- mime content type to
excludedContentTypesForCanonicalization property. This is applicable only for
AS2 transactions as there is no canonicalization support provided for RNIF
transactions.
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IBM WebSphere Partner Gateway Enterprise and Advanced Editions: Administration Guide