Redocly OpenAPI structure error. Property `openapi` is not expected here

Question

I am trying to create an api documentation using redocly.

On my openapi.yaml it is linking to a yaml that has the api docs called kpi-documentation.yaml

link/$ref in openapi.yaml

  /kpiDocumentation:
    $ref: paths/kpi-documentation.yaml

I have an error in my visual studio code redocly preview extension that says

We found structural problems in your definition, please check the files below before running the preview.
File: /Users/xx/Desktop/Projects/api-docs/openapi/paths/kpi-documentation.yaml
Problem: Property `openapi` is not expected here.

File: /Users/xx/Desktop/Projects/api-docs/openapi/paths/kpi-documentation.yaml
Problem: Property `info` is not expected here.

File: /Users/xx/Desktop/Projects/api-docs/openapi/paths/kpi-documentation.yaml
Problem: Property `paths` is not expected here.

File: /Users/xx/Desktop/Projects/api-docs/openapi/paths/kpi-documentation.yaml
Problem: Property `components` is not expected here. 

Part of code that I have in the kpi-documentation.yaml that appears to be throwing the error is

openapi: "3.1"
info:
  title: KPI API
  version: '1.0'
  description: Documentation of API endpoints of KPI
servers: 
  - url: https://api.redocly.com
paths:

I have checked the documentation on the redocly website and it looks like my yaml structure is fine.

Also to note the kpi-documentation previews fine by itself when using the preview, but not when I preview the openapi.yaml which is the root file that needs to work.

https://redocly.com/docs/openapi-visual-reference/openapi/#OAS-3.0

rootfile

openapi.yaml

openapi: 3.1.0
info:
  version: 1.0.0
  title: KPI API documentation
  termsOfService: 'https://example.com/terms/'
  contact:
    name: Brendan
    url: 'http://example.com/contact'
  license:
    name: Apache 2.0
    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
  x-logo:
    url: 'https://www.feedgy.solar/wp-content/uploads/2022/07/Sans-titre-1.png'
tags:
  - name: Insert Service 1
    description: Example echo operations.
  - name: Insert Service 2
    description: Operations about users.
  - name: Insert Service 3
    description: This is a tag description.
  - name: Insert Service 4
    description: This is a tag description.
servers:
  - url: 'https://{tenant}/api/v1'
    variables:
      tenant:
        default: www
        description: Your tenant id
  - url: 'https://example.com/api/v1'
paths:
  '/users/{username}':
    $ref: 'paths/users_{username}.yaml'
  /echo:
    $ref: paths/echo.yaml
  /pathItem:
    $ref: paths/path-item.yaml
  /pathItemWithExamples:
    $ref: paths/path-item-with-examples.yaml
  /kpiDocumentation:
    $ref: 'paths/kpi-documentation.yaml'

pathitem file

kpi-documentation.yaml

openapi: "3.1"
info:
  title: KPI API
  version: '1.0'
  description: Documentation of API endpoints of KPI
servers: 
  - url: https://api.redocly.com
paths:
  "/api/v1/corrected-performance-ratio/plants/{id}":
    get:
      summary: Same as the Performance Ratio, but the ratio is done using Corrected Reference Yield, so it considers thermal losses in the panels as normal. The WCPR represents the losses in the BoS (balance of system), so everything from the panel DC output to the AC output. 
      operationId: corrected_performance_ratio_plants_retrieve
      parameters:
        - in: query
          name: date_end
          schema:
            type: string
            format: date
          required: true
        - in: query
          name: date_start
          schema:
            type: string
            format: date
          required: true
        - in: query
          name: frequency
          schema:
            enum:
              - H
              - D
              - M
              - Y
            type: string
            default: H
            minLength: 1
        - in: path
          name: id
          schema:
            type: integer
          description: A unique integer value identifying this plant.
          required: true
        - in: query
          name: threshold
          schema:
            type: integer
            default: 50
      tags:
        - corrected-performance-ratio
      security:
        - tokenAuth: []
        - cookieAuth: []
        - {}
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/KPIResponse"
          description: ""
  "/api/v1/corrected-performance-ratio/plants/{id}/inverters":