Webhook cURL encoding problem (Windows)

I’m trying to figure out how to send a table to a channel via cURL (on windows) using a webhook.

My command currently looks like this:

curl -i -X POST -H “Content-Type: application/json; charset=UTF-8” -d @mm.json https:/my.secret/hooks/abcdefg

The code for the table is in the mm.json file. It is also successfully transferred to the channel but is displayed as a normal message and not as a table. therefore iIsuspect a encoding problem.
If I send the code from the .json file directly into the channel it will be converted correctly into a table.

My table code from the mm.json file:

  "text": "#### Test results for July 27th, 2017\n<!channel> bitte folgende Fehler\n
  | Datum      | Uhrzeit     | Meldung                                        |
  | Server     | 948         | :white_check_mark: 0                           |
  | Web Client | 123         | :warning: 2 [(see details)]|
  | iOS Client | 78          | :warning: 3 [(see details)]|