How can i debug why files are not being created when using migrate files to media module?

Question

I run the drush migrate-duplicate-file-detection migd8_grants_media_step1 successfully, and then run the node migration and step 1, however the media is being populated with the name only, the file is not attached nor are the files being moved over to the sites default/files/grants directory as they should Steps to reproduce

this is my step 1 yml.

# File to Media Migration configuration for grants Media migration

id: migd8_grants_media_step1
label: Grants Media Step 1
migration_group: cncs
source:
  key: migrate
  plugin: media_entity_generator_d7
  entity_type: node
  bundle: grants
  langcode: und
  d7_file_url: 'https://www.externalwebsite/sites/default/files/'
  field_names:
  - field_files

destination:
  plugin: entity:media

process:

  bundle:
    plugin: default_value
    default_value: document

# Using the alt tag if available, else the file name.
  name:
    plugin: media_name
    source: file_name

# This process plugin will skip the whole row if a existing media is found.
  existing_media_file:
    plugin: check_media_duplicate
    source: target_id

# This process plugin will skip the whole row if a duplicate document is found.
  unique_file_id:
    plugin: check_duplicate
    source: target_id

# Map the field
field_media_document/target_id: target_id
field_media_document/target_id:
  plugin: media_file_copy
  move: FALSE
  reuse: TRUE
  path: 'public://grants/'
  source: file_path

langcode: und

uid:
  plugin: default_value
  default_value: 1

Answer 1

You have an an error in your yml file, should be:

# Map the field
field_media_image/title: title
field_media_image/target_id:
    plugin: media_file_copy
    move: FALSE
    reuse: TRUE
    path: 'public://grants/'
    source: file_path

langcode: langcode

Answer 2

the answer was that i had to put the nid in the import so the nid was the same in the source and target content in order for this to work.