Use Migrate Tools to import into multiple value link field from JSON array

I am trying to import data into a multi-value link field from a JSON source using Migrate Tools. I think I should be able to do this without writing a custom plugin, but so far nothing is working. My JSON looks like this:

[
 {
  "first_name": "Joe"
  "last_name": "Smith"
  "departments": [
     {
       "department_name": "Mail room"
       "department_url": "https://myoffice.com/mailroom"
     },
     {
       "department_name": "Receiving"
       "department_url": "https://myoffice.com/receiving"
     }
   ],
 },
 { . . . etc }
]

The department_name and department_url values would be the title value and uri value for a multi-value link field. I have tried using the sub_process plugin by configuring the migration config this way:

- name: department_data
  label: "Department data"
  selector: departments

...

process:
   field_department_link:
      plugin: sub_process
      source: department_data
      process:
        'field_department_link/title': department_name
        'field_department_link/uri': department_url

I should note that this migration config is working overall, as I have a number of straight-up text fields that are importing just fine, so I know the issue is specific to how I'm trying to handle this particular field. Also please note that I don't have any control over the JSON itself. It's generated by a third-party application to which I don't have access.

Got it figured out. Here's the process section of the config file for the multi-value link field:

process:
  field_department_link:
    plugin: sub_process
    source: department_data
    process:
      uri: department_url
      title: department_name