Multipath bond not working

Hello all
I am having issues with setting up multipath over two path with one primary (eth0) and one spare (eth1)
I’m on Ubuntu 20.04, running ZT 1.6.4

Here is my /var/lib/zerotier-one/local.conf file:

{
"settings":
{
"defaultBondingPolicy": "active-backup",
    "active-backup":
    {
      "linkSelectMethod": "always",
      "links":
      {
        "eth0": { "failoverTo": "eth1", "mode": "primary" },
        "eth1": { "mode": "spare" }
      }
    }
  }

Listing the bonds gives me this:

$ sudo zerotier-cli bond list
zerotier-cli bond list
    <peer>                        <bondtype>    <status>    <links>
3d806e5c44                     active-backup     HEALTHY        2/2

But showing the bond shows it as degraded for some reason, and without any link where just before it showed two… Running the previous line again gives the same result, so it’s not just disconnecting in between running the two lines

$ sudo zerotier-cli bond 3d806e5c44 show
Peer               : 3d806e5c44
Bond               : -
Link Select Method : 0
Status             : Degraded
Links              : 0/0
Failover Interval  : 0 (ms)
Up Delay           : 0 (ms)
Down Delay         : 0 (ms)
Packets Per Link   : 0 (ms)

Sadly I had a similar problem and got no help.
If you ever get it to work, please let me know!