Create file on-prem Sharepoint: Error 502 Bad Gateway

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Hello,

I'm unable to Create File in an on-prem Sharepoint doc library. 

- Using Sharepoint Create File action in Flow

- Created a new connection selecting "On prem data gateway"

- Tried by Windows username alone and servername\username, same error

- Flow runs for ~10-15mins before timing out

How do I troubleshoot this?

Error message: 

{
  "error": {
    "code": 502,
    "source": "flow-apim-msmanaged-na-westus2-01.azure-apim.net",
    "clientRequestId": "11f81548-2670-4fc2-a7b2-c13cb18fb0d7",
    "message": "BadGateway",
    "innerError": {
      "status": 502,
      "message": "Received error payload from gateway service with ID 102446: Error parsing UserName '<pi>windowsUN</pi>'..\r\nclientRequestId: 11f81548-2670-4fc2-a7b2-c13cb18fb0d7",
      "source": "https://sharepointonline-ncus.azconn-ncus.p.azurewebsites.net/datasets/https%253A%252F%252Fonpremsp.company.com%252Fteam%252Fdata%252F/files?folderPath=%2FShared%20Documents%2F&name=test.png&queryParametersSingleEncoded=true",
      "errors": []
    }
  }
}