Restore of playlists backup using POST REST API fails

Dear Volumio community
I’m using a Raspberry PI 2 and Volumio version 2.246
Everything went fine so far and I’m preparing a clean recovery SD card now

For that purpose I would like to backup my playlists and webradios -> That went well
But restoring them over the REST API with a POST call returns an error
for all type, path and data combinations I tried.

I’m using the RESTED client Add-On for firefox
The last try for a POST request was:

URL: volumio.local/api/v1/restore/playlists
Method: POST
appl/type: JSON
type: playlist
data: [{“name”:“80’s”,“content”:[{“service”:“mpd”,“type”:“song”,“title”: … }]

The value for data is the value of object “backup” from the API GET playlists response

I get a 200 OK response with the header content
“Error”: “Error: impossible to restore given data”

----- Update -----
If I just use one playlist like { “name”:"Playlist, “content”[…json-content here…]},
I get a success message back

“Message”: “Succesfully restored resource”

But still: No Playlist or WebRadio is found in Volumio - Browse …

Any help what I’m missing here or where I do the wrong thing is highly appreciated.
I really don’t have any clue where I run into the wrong directio or what else I can try.

Thanks a lot in advance