"multiple ids not supported" error when used with micromdm

[meta-github]

How it should be:

When updating a declaration, the ddm server should notify all clients that are enrolled with that declaration.

What I observed:

While processing the update of the declaration, the kmfddm server does update its content of the declaration. New assignments to clients that had not been assigned to that declaration before will get the updated version. But (and here is the problem), for existing clients, no update notification is send to clients, if more than one client is enrolled to that declaration.

To reproduce:

1. use kmfddm with micromdm
2. create a set and assign that set to two clients
3. create a declaration and assign that to the set
4. update the declaration -> boom, error "multiple ids not supported" is thrown and clients are not updated

Tested with kmfddm v0.4.1 and micromdm v1.11.0, both running on macOS 14.3.