RPC Fields Don't Show in Array Aggregator Target structure type

[giladba]

I implemented a module with the following mappable parameters:

[
  {
    "name": "contacts",
    "type": "array",
    "label": "Contacts",
    "spec": [
      {
        "name": "firstName",
        "type": "text",
        "label": "First Name",
        "required": false
      },
      {
        "name": "lastName",
        "type": "text",
        "label": "Last Name",
        "required": false
      },
      {
        "name": "phoneNumber",
        "type": "text",
        "label": "Phone Number",
        "required": false
      },
      "rpc://listContactFields"
    ]
  }
]

Note the use of an RPC.

I am using this module to import contacts details from a Google sheet.
I am using an array aggregator between the Google sheet module and my module like so:

In the input to my module (the last module) I can see the field fetched by the RPC (“Dog Name”):

However, I don’t see it in the Target structure type of the Array aggregator, where only the hardcoded fields are shown. So I cannot map anything to it.