@olivierlambert Done: https://github.com/vatesfr/xen-orchestra/commit/33b45d2eda2ce6d8071541da246bdcfd06b133b8
It's not perfect but that should help 
Example:
vm.start
{
  "id": "123e4f2b-498e-d0af-15ae-f835a1e9f59f",
  "bypassMacAddressesCheck": false,
  "force": false
}
{
  "errors": [
    "R620-L3: VM_REQUIRES_SR(OpaqueRef:21fa00fc-62ce-4694-8b49-fcecd600a89e, OpaqueRef:4dd615a7-9a8c-4698-aceb-c10f782321c8)",
    "R620-L1: HOST_NOT_ENOUGH_FREE_MEMORY(216430280704, 18778341376)",
    "R620-L2: VM_REQUIRES_SR(OpaqueRef:21fa00fc-62ce-4694-8b49-fcecd600a89e, OpaqueRef:4dd615a7-9a8c-4698-aceb-c10f782321c8)"
  ],
  "message": "",
  "name": "Error",
  "stack": "Error: 
    at Xapi._startVm (file:///home/julien/dev/vatesfr/xen-orchestra/packages/xo-server/src/xapi/index.mjs:1358:15)
    at Xapi.startVm (file:///home/julien/dev/vatesfr/xen-orchestra/packages/xo-server/src/xapi/index.mjs:1393:7)
    at Api.callApiMethod (file:///home/julien/dev/vatesfr/xen-orchestra/packages/xo-server/src/xo-mixins/api.mjs:307:20)"
}
2 
julien-f committed  to vatesfr/xen-orchestra
feat(xo-server): better info when failing to start a VM
Fixes https://xcp-ng.org/forum/post/47329