https://understanddrupal.com/articles/migrating-json-files-drupal

image_migration_process.yml

process:
  psf_destination_filename:
    plugin: callback
    callable: basename
    source: src_photo_url

node_migration_process_destination_and_dependencies.yml

process:
  field_ud_image/target_id:
    plugin: migration_lookup
    migration: udm_json_source_image
    source: src_photo_file
destination:
  plugin: 'entity:node'
  default_bundle: ud_paragraphs
migration_dependencies:
  required:
    - udm_json_source_image
    - udm_json_source_paragraph
  optional: []

paragraph_migration_process.yml

process:
  field_ud_book_paragraph_title: src_book_title
  field_ud_book_paragraph_author: src_book_author

udm_book_paragraph_sample.json

{
  "data": {
    "udm_book_paragraph": [
      {
        "book_id": "B10",
        "book_details": {
          "title": "The definite guide to Drupal 7",
          "author": "Benjamin Melançon et al."
        }
      },
      {...},
      {...}
    ]
}

udm_data_sample.json

{
  "data": {
    "udm_people": [
      {
        "unique_id": 1,
        "name": "Michele Metts",
        "photo_file": "P01",
        "book_ref": "B10"
      },
      {...},
      {...}
    ],
    "udm_book_paragraph": [
      {
        "book_id": "B10",
        "book_details": {
          "title": "The definite guide to Drupal 7",
          "author": "Benjamin Melançon et al."
        }
      },
      {...},
      {...}
    ],
    "udm_photos": [
      {
        "photo_id": "P01",
        "photo_url": "https://agaric.coop/sites/default/files/pictures/picture-15-1421176712.jpg",
        "photo_dimensions": [240, 351]
      },
      {...},
      {...}
    ]
  }
}

udm_json_source_image_source.yml

source:
  plugin: url
  data_fetcher_plugin: file
  data_parser_plugin: json
  urls:
    - modules/custom/ud_migrations/ud_migrations_json_source/sources/udm_data.json
  item_selector: /data/udm_photos
  fields:
    - name: src_photo_id
      label: 'Photo ID'
      selector: photo_id
    - name: src_photo_url
      label: 'Photo URL'
      selector: photo_url
  ids:
    src_photo_id:
      type: string

udm_json_source_node_local_source.yml

source:
  plugin: url
  data_fetcher_plugin: file
  data_parser_plugin: json
  urls:
    - modules/custom/ud_migrations/ud_migrations_json_source/sources/udm_data.json
  item_selector: /data/udm_people
  fields:
    - name: src_unique_id
      label: 'Unique ID'
      selector: unique_id
    - name: src_name
      label: 'Name'
      selector: name
    - name: src_photo_file
      label: 'Photo ID'
      selector: photo_file
    - name: src_book_ref
      label: 'Book paragraph ID'
      selector: book_ref
  ids:
    src_unique_id:
      type: integer

udm_json_source_node_remote_source.yml

source:
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: json
  urls:
    - https://api.myjson.com/bins/110rcr
  item_selector: /data/udm_people
  fields: ...
  ids: ...

udm_json_source_paragraph_source.yml

source:
  plugin: url
  data_fetcher_plugin: file
  data_parser_plugin: json
  urls:
    - modules/custom/ud_migrations/ud_migrations_json_source/sources/udm_data.json
  item_selector: /data/udm_book_paragraph
  fields:
    - name: src_book_id
      label: 'Book ID'
      selector: book_id
    - name: src_book_title
      label: 'Title'
      selector: book_details/title
    - name: src_book_author
      label: 'Author'
      selector: book_details/author
  ids:
    src_book_id:
      type: string

udm_people_sample.json

{
  "data": {
    "udm_people": [
      {
        "unique_id": 1,
        "name": "Michele Metts",
        "photo_file": "P01",
        "book_ref": "B10"
      },
      {...},
      {...}
    ]
  }
}

udm_photos_sample.json

{
  "data": {
    "udm_photos": [
      {
        "photo_id": "P01",
        "photo_url": "https://agaric.coop/sites/default/files/pictures/picture-15-1421176712.jpg",
        "photo_dimensions": [240, 351]
      },
      {...},
      {...}
    ]
  }
}