servicenow-powershell
                                
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                        Add-ServiceNowAttachment Error - "Item has already been added. Key in dictionary: 'Content-Type' Key being added: 'Content-Type'"
Hiya, Not sure if Add-ServiceNowAttachment is supposed to do multiple files.
If it is, I think the Content-Type header might be duplicated in the ForEach loop here:
https://github.com/Snow-Shell/servicenow-powershell/blob/19e38411ee978aff2581eb06f5cdb2827042a289/ServiceNow/Public/Add-ServiceNowAttachment.ps1#L173
I think with multi-file you'll want the type to be multipart or octet-stream. Haven't tried fixing it yet, currently just working around by sending one file at a time.
Environment
Operating System: Windows Powershell
ServiceNow module version: 3.4.1
PowerShell version:  5.1
Steps to reproduce
Use a splat containing two filepath
$addServiceNowAttachmentSplat = @{
    ID          = $Ticket.Number
    Table       = 'incident'
    File        = $LogFilePath, $OutputFilePath
}
Add-ServiceNowAttachment @addServiceNowAttachmentSplat
Expected behavior
Multiple files upload to service now incident
Actual behavior
First item is uploaded, next files generate error "Item has already been added. Key in dictionary: 'Content-Type' Key being added: 'Content-Type'"
Screenshots

Thanks for reporting this @JasonDTX. Would you mind testing the fix #208?
Looks good, posting in 208, closing 207.