olivierlambert I know I'm chiming in here quite late but I'm also facing the same issue, and the machine uuid is not on the destination server.

I have 3 xcp-ng servers, I want to migrate from Server C to B, all 3 are independent pools and the same XCP-NG version.

da010bca-fa81-629c-5b25-ea16f03e9510 is the UUID of the VM I'm looking to move

Server C:
uuid ( RO)           : 4104416d-2539-411d-8d73-3590865eca4d
     name-label ( RW): Control domain on host: localhost
    power-state ( RO): running


uuid ( RO)           : da010bca-fa81-629c-5b25-ea16f03e9510
     name-label ( RW): AZUREDIRSYNC
    power-state ( RO): running

Server B:

uuid ( RO)           : 907bf603-49df-dc36-fc9a-9bb706f12cc8
     name-label ( RW): F2VMSBODOOIT001
    power-state ( RO): halted


uuid ( RO)           : 62d721e2-0ef0-4d37-5858-d754369825f7
     name-label ( RW): F2VMSBSSOXIT002
    power-state ( RO): running


uuid ( RO)           : 7af2c68c-7fde-c3c3-38a3-3e107412537e
     name-label ( RW): xenorchestrav2
    power-state ( RO): running


uuid ( RO)           : 695a14bf-37f0-05b5-7141-ed1be479b0de
     name-label ( RW): Spiceworks-Fourman-Household
    power-state ( RO): running


uuid ( RO)           : 9c13dfc9-0e57-4da0-93dd-8bbfbc850cb4
     name-label ( RW): Control domain on host: localhost
    power-state ( RO): running


uuid ( RO)           : 6cd8e824-a5c0-c521-9f1d-bf768e3b9999
     name-label ( RW): F2VMSBODOOIT001_2021-04-01T21:40:16.406Z
    power-state ( RO): halted


uuid ( RO)           : 82c805a7-e79a-6d85-8ad6-1e8a08efce23
     name-label ( RW): F2VMSBWADMIT001
    power-state ( RO): halted


uuid ( RO)           : f0d98192-bb27-129a-4cec-7ef9d4dac880
     name-label ( RW): F2VMSBDBNOIT004
    power-state ( RO): halted


uuid ( RO)           : 35357e77-8a48-f523-5abd-dbb1da560b00
     name-label ( RW): F2VMSBINVXIT001
    power-state ( RO): running


uuid ( RO)           : 350e0434-2cab-c3eb-0d22-48d4f38d7997
     name-label ( RW): F2VMSBWWWXIT001
    power-state ( RO): running


uuid ( RO)           : 4db452a8-a06d-ff74-3ddb-7df3fad3e1c5
     name-label ( RW): F2VMSBSSOXIT001
    power-state ( RO): running


uuid ( RO)           : 5d229ce2-9a31-aabe-d250-7f1ff377c551
     name-label ( RW): F2VMSBODOOIT001_2021-04-01T18:53:52.769Z
    power-state ( RO): halted

Getting the following error in both xcp-ng center and XO:

vm.migrate
{
  "vm": "da010bca-fa81-629c-5b25-ea16f03e9510",
  "mapVdisSrs": {
    "dd58e003-a906-420f-8f41-a96d1d42e087": "41587f9b-a755-03f8-1fa1-e80d18c2e8b1"
  },
  "mapVifsNetworks": {
    "b37022e9-031d-04aa-f574-92102095b6ad": "89375484-4323-e6c1-542b-cb993b4272c4"
  },
  "migrationNetwork": "93b5130a-6c13-9218-9588-582a9379bef4",
  "sr": "41587f9b-a755-03f8-1fa1-e80d18c2e8b1",
  "targetHost": "126c62b2-aacb-4f5a-b6bc-12865592ed20"
}
{
  "code": 21,
  "data": {
    "objectId": "da010bca-fa81-629c-5b25-ea16f03e9510",
    "code": "DUPLICATE_VM"
  },
  "message": "operation failed",
  "name": "XoError",
  "stack": "XoError: operation failed
    at factory (/opt/xen-orchestra/packages/xo-common/src/api-errors.js:21:32)
    at /opt/xen-orchestra/packages/xo-server/src/api/vm.js:487:15
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at runNextTicks (internal/process/task_queues.js:62:3)
    at processImmediate (internal/timers.js:434:9)
    at process.topLevelDomainCallback (domain.js:144:15)
    at process.callbackTrampoline (internal/async_hooks.js:129:14)
    at Object.migrate (/opt/xen-orchestra/packages/xo-server/src/api/vm.js:474:3)
    at Api.callApiMethod (/opt/xen-orchestra/packages/xo-server/src/xo-mixins/api.js:304:20)"
} 

Thanks,
Dan