External Services can be invoked from Flows.

1. Go to https://app.swaggerhub.com/home and Sign Up for Trial.

2. Create an API using “Create New API” option in Swagger.

3. Enter the API details and click “Create API Swagger” button.

4. Use the following specification to create the API.

openapi: 3.0.0
info:
  version: '1'
  title: ''
  description: Employee Search API
paths:
  /employee:
    get:
      tags:
        - EmployeeAPI
      summary: API to search employees
      operationId: searchEmployee
      description: |
        You can search for an employee in the system
      parameters:
        - in: query
          name: employeeNo
          description: Employee Number to search in the system
          required: true
          schema:
            type: string
      responses:
        '200':
          description: search results matching criteria
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Employee'
        '400':
          description: bad input parameter
components:
  schemas:
    Employee:
      type: object
      required:
        - empNo
        - employeeName
        - employeeAge  
        - employeeJoiningDate  
      properties:
        empNo:
          type: string
          format: uuid
          example: emp-01
        employeeName:
          type: string
          example: Test Name
        employeeAge:
          type: number
          example: 19
        employeeJoiningDate:
          type: string
          format: date
          example: '2015-01-01'
servers:
  # Added by API Auto Mocking Plugin
  - description: SwaggerHub API Auto Mocking
    url: https://virtserver.swaggerhub.com/<YOUR_USERNAME>/Employee/1

5. Publish the API.

6. Export the API.

7. Create a Salesforce External Credential.

8. Create a Salesforce Named Credential.

9. Create a Salesforce Permission Set.

10. In the Permission Set, give access to User External Credentials object.

11. Assign the Permission to the users who will be accessing the External Service.

12. In the External Credential, click New button on the Permission Set Mappings section.

13. Assign the Permission Set to the External Credential.

14. Create an External Service using New External Service button in Salesforce.

15. Use From API Specification.

16. Use Complete JSON as the Service Schema and use the JSON exported from the Swagger.

17. Select the searchEmployee operation.

18. Use the searchEmployee action in the Flow to test.

Output: