Convert Downloaded API Backup to readable .zip file

Convert Downloaded API Backup to readable .zip file

Hello,

has somebody an idea how to convert the result of an API request for an backup into the readable .zip file?
I work with PowerShell and I got the API working so that I get a response from /crm/bulk/v4/backup/urls and from the corresponding URLs that are returned. 
When I try to save the received data as a .zip file, the file can't be opened.

Has someone got this working?