Two fields are defined the same way. Why is only one receiving a validation error?

I am adding the field 'accountType' to our yaml files, with the same setup as an existing field 'status', but getting an error when calling a GET /accounts endpoint in Postman with status and accountType as filters.

From yaml:

paths:
  /accounts:
    get:
      operationId: getAccounts
      summary: Retrieve a list of accounts
      tags:
      - accounts
      parameters:
      - $ref: '#/components/parameters/accountName'
      - $ref: '#/components/parameters/status'
      - $ref: '#/components/parameters/accountType'
      responses:
        '200':
          $ref: '#/components/responses/Accounts'
        '400':
          $ref: '#/components/responses/BadRequest'
        '401':
          $ref: '#/components/responses/Unauthenticated'
        '500':
          $ref: '#/components/responses/InternalServerError'

components:
  schemas:
    Account:
      type: object
      properties:
        accountId:
          type: string
          description: unique identifier for the accounts
          readOnly: true
        name:
          type: string
          description: unique user friendly display name for an account
          minLength: 3
          maxLength: 100
        status:
          type: string
          description: status for an account
          enum: ['Active', 'Disabled', 'Merged']
        accountType:
          type: string
          description: specifies type of account within the company ecosystem.
          enum: ['Owner', 'Partner', 'Maker', 'Buyer', 'Unknown']

    ValidStatus:
      type: array
      items:
        type: string
        enum: ['Active', 'Disabled', 'Merged']
      uniqueItems: true

    ValidAccountType: 
      type: array
      items:
        type: string
        enum: ['Owner', 'Partner', 'Maker', 'Buyer', 'Unknown']
      uniqueItems: true

  parameters:
    status:
      name: status
      in: query
      description: Filters account list with specified status
      required: false
      explode: false
      schema:
        $ref: '#/components/schemas/ValidStatus'

    accountType:
      name: accountType
      in: query
      description: Filters account list with specified type
      required: false
      explode: false
      schema:
        $ref: '#/components/schemas/ValidAccountType'

Query without accountType filter:

{{baseUrl}}/accounts?status=Active&fields=status,accountType

Results:

Status: 200 OK

Content:
{
  count: 2,
  items: [
    {
      accountId: 1,
      name: 'test1'
      status: 'Active'
      accountType: 'Maker'
    },
    {
      accountId: 3,
      name: 'test3'
      status: 'Active'
      accountType: 'Owner'
    }
  ]
}

Query with accountType filter:

{{baseUrl}}/accounts?status=Active&accountType=Maker&fields=status,accountType

Error:

{
    "title": "BadRequestError",
    "status": 400,
    "detail": "Error while validating request: request.query.accountType should be array",
    "type": "http://localhost:10080/api/v1/errorTypes/BadRequestError",
    "_links": {
        "type": {
            "href": "http://localhost:10080/api/v1/errorTypes/BadRequestError"
        }
    }
}

Why is the validation complaining about accountType, when status is setup exactly the same but with no error?