Does anyone have any idea what's causing this to show up? Given that the file extension .cdxml is a permitted file extension in the environment and the user has confirmed that the file type matches the extension.
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Appian tries to read the file you uploaded it tries to match whether contents match it's file type. Are you sure your file is cdxml type.
I found this other thread where Mike explained it very clearly (It might help you to resolve the issue)
https://community.appian.com/discussions/f/general/23862/the-file-s-extension-png-does-not-match-its-underlying-file-type
The file is of cdxml type. . Thanks for the link to Mike's thread. Seems a like a support case is needed in this case.
https://docs.appian.com/suite/help/25.1/Appian_Administration_Console.html#using-file-type-verification-effectively
per OP's screenshot above, it looks like the feature is probably malfuncitoning.
Not sure what Appian uses in the backend but it may just be that the "magic mime type" detection misbehaving.
In those cases, your only option is to deactivate that feature or rename the file to another extension for which the detection does not trigger.
yeah, i assume in this case it might be a case of different types being implemented manually, and since there's basically no consistency in how different file types identify them in the first few bytes of a file (see the gross disparity between "png" and "jpg" even, in my screenshot in the other thread), there might just be a limit to how many / how well supported super-niche types are (and afaik "cdxml" would count as a niche type).