I'm on Windows, so the quotes are a different kind for me, but this worked for me:
curl -L -H "X-Cisco-Meraki-API-Key: azertyuiop123456789" -X POST "https://api.meraki.com/api/v0/networks/L_123456789/cameras/A11A-B22B-C33C/snapshot"
You don't seem to have the -L in there, it's important because this is a POST request, and these tend to need to follow the redirects.