Automatic index snapshot example doesn't work

I’m using opendistro 7.4 and I’m trying to build a a policy that have a snapshot of some indices after certain time. I have seen that there is an example in the official develop guide:

  "policy": {
    "description": "Takes an index snapshot.",
    "schema_version": 1,
    "default_state": "empty",
    "states": [{
        "name": "empty",
        "actions": [],
        "transitions": [{
          "state_name": "occupied",
          "conditions": {
            "min_doc_count": 1
        "name": "occupied",
        "actions": [{
          "snapshot": {
            "repository": "<my-repository>",
            "snapshot": "<my-snapshot>"
          "transitions": []

Unfortunely this command returns to me an error:

Invalid field: [snapshot] found in Action

Could someone please help me to implement automatic snapshot?
Thank you

Your opendistro version may not be supported for snapshot operation in index management.
Check opendistro version history.
Opendistro adds snapshot operation at 1.8.0(es version 7.7).
If you can not upgrade your opendistro version, try curator.