Hi Dominic,
I would recommend to perform the below steps :
1. Place the downloaded SAR file in download directory (same directory where stack.xml is placed).
2. Extract the SAR file in G:\EHP5_EHP7\SUM\abap\exe\ directory.
3. Make sure in the download directory , there are no additional extra dbatools SAR file other than correct SAR file.
Best Regards,
Gaurav