JSON:API to Migrating Taxonomy References isn't mapping

OK, for a number of reasons I'm doing a Drupal 8 - Drupal 8 migration using the JSON:API module on the source site. I've run into an issue attaching taxonomy terms to nodes. Here's as far as I've gotten :

1) I created a vocabulary called "Photo Categories"

2) I've created and run import_drupal_taxonomy_photo_categories to import the terms. This works perfectly. I have manually checked to ensure they all get in. I use the UUID as the migration's unique identifier.

3) I have a content type called Photos, it has a field called Photo Category which references the Photo Categories vocabulary.

4) From the source JSON in the relationships section I see this:

"field_photo_category": { "data": [ { "type": "taxonomy_term--photo_categories", "id": "84c1e8bd-16f7-429f-b299-50fe43297d47" }, { "type": "taxonomy_term--photo_categories", "id": "00931a31-d129-4c55-a962-f7ba11fed5a4" } ], "links": { "self": "https:\/\/seanreiser.com\/jsonapi\/node\/photo\/1396b571-0ece-4a07-ab17-7327e030dfb5\/relationships\/field_photo_category", "related": "https:\/\/seanreiser.com\/jsonapi\/node\/photo\/1396b571-0ece-4a07-ab17-7327e030dfb5\/field_photo_category" } } 

5) In the source > Fields section of import_drupal_type_photo I have:

- name: field_photo_category label: 'Field Photo Category' selector: /relationships/field_photo_category/data 

6) In the process section I have:

 field_photo_category: plugin: iterator source: field_photo_category process: plugin: migration_lookup migration: import_drupal_taxonomy_photo_categories source: id 

As I understand it this should loop through the field_photo_category.data and do a migration lookup on each id. But nothing is getting mapped.

I have verified that the ids match the ids in the data section match the UUID from the taxonomy term JSON. I have checked the database and verfied that ids appear in migrate_map_import_drupal_taxonomy_photo_categories.soure1 and they map to the appropriate tids.

I have installed the migrate devel module and when I run the migration with --migrate-debug this is what the destination section look like:

 'field_photo_category' => array (2) [ array (1) [ 'source' => string (36) "84c1e8bd-16f7-429f-b299-50fe43297d47" ] array (1) [ 'source' => string (36) "00931a31-d129-4c55-a962-f7ba11fed5a4" ] ] 

So, my question, what am I doing wrong? I have the rest of this part of my migration laid out and this seems to be the final obstacle.

Thanks in Advance