Using PO_EXPRESS_CI to add comment, but COMMENT_TYPE is always blank

I am using the CI to add a comment to a PO Line. It works, but the COMMENT_TYPE, which I set to "LIN" is always blank when I look at the data. And thus the comment does not show on the PO in PeopleSoft. If I SQL Update the value to "LIN" then I can see it in PeopleSoft. The XML I'm sending is below. The record has all the values I send in except COMMENT_TYPE. I feel like I'm missing something important, but have no idea what.

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">