Migrate source id's and map them to already existing Drupal entity id's I've tried a bunch of different setups, but I can't get it to work. Here are the two setups I was the most confident in that it would work. I simply want to map existing id's in the source to new id's that are already created in taxonomy. 

Attempt 1: 

  field_season:
    # Map the seasons to our already existing taxonomy terms
    -
      plugin: static_map
      source: season
      map:
        '1': 26 # Lente
        '2': 29 # Zomer
        '3': 24 # Herfst
        '4': 28 # Winter
    -
      plugin: entity_lookup
      value_key: tid
      entity_type: taxonomy_term
      bundle_key: tid
      bundle: seasons


Attempt 2: 

  field_season:
    plugin: iterator
    source: field_season
    process:
      target_id:
        # Map the seasons to our already existing taxonomy terms
        plugin: static_map
        source: season
        map:
          '1': 26 # Lente
          '2': 29 # Zomer
          '3': 24 # Herfst
          '4': 28 # Winter


Edit: FWIW, all the other processes work just fine!
This happens to me all the time, I post a question after fiddling around for hours and shortly after, I manage to find the answer myself. It appears that the first attempt was almost right. Though bundle_key should be vid, I'm not sure why though.

The config, for completeness sake.

  field_season:
    # Map the seasons to our already existing taxonomy terms
    -
      plugin: static_map
      source: season
      map:
        '1': 26 # Lente
        '2': 29 # Zomer
        '3': 24 # Herfst
        '4': 28 # Winter
    -
      plugin: entity_lookup
      value_key: tid
      entity_type: taxonomy_term
      bundle_key: vid
      bundle: seasons