Error when trying to configure buffering

[hightwoltt]

I'm trying to set up buffering, in case the intermediate Vector host is unavailable.
Below is my sinks configuration:

sinks:

  intermediary_vector:
    type: vector
    inputs:
      - add_host

   buffer:
      type: disk
      max_size: 1GiB
      when_full: block
    address: "192.168.8.103:9009"

After restarting the Vector container, I get the error:
ERROR vector::cli: Configuration error. error=did not find expected key at line 46 column 4, while parsing a block mapping at line 41 column 3

Please tell me what could be the reason? or how to do buffering in a different way? Thanks!