OpenIntegrations/docs/en/examples/Slack/UploadFile.txt

    Token   = FunctionParameters["Slack_Token"];
    Channel = FunctionParameters["Slack_Channel"];
    File    = FunctionParameters["Document"]; // URL, Binary Data or File path

    FileName = "megadoc.docx";
    Title    = "NewFile";

    Result = OPI_Slack.UploadFile(Token, File, FileName, Title);

    Result = OPI_Slack.UploadFile(Token, File, FileName, Title, Channel);