> ## Documentation Index > Fetch the complete documentation index at: https://sendcloud.dev/llms.txt > Use this file to discover all available pages before exploring further. # Start OAuth2 authorization > Initiate the OAuth2 authorization flow for a connection that requires it (e.g., Klaviyo). Returns an authorization URL to redirect the user to. Start the OAuth2 authorization flow for a Klaviyo connection. This endpoint returns an authorization URL that the user should be redirected to in their browser. After the user authorizes access, the OAuth provider will redirect back to the Sendcloud callback URL, completing the connection setup. Use the [Create a connection](/api/v3/event-subscriptions/create-a-connection) endpoint with `type: "klaviyo"`. Call this endpoint to get the authorization URL. Open the `authorization_url` in the user's browser to complete the OAuth2 flow. ## OpenAPI ````yaml /.openapi/v3/event-subscriptions/openapi.yaml post /event-subscriptions/connections/{id}/authorization openapi: 3.1.0 info: title: Event Subscriptions API version: 3.0.0 description: >- **BETA** - The Event Subscriptions API allows you to subscribe to parcel events and have them delivered to external endpoints such as webhooks or Klaviyo. This API uses a two-part model: - **Connections** define _where_ events are delivered (e.g., a webhook URL or a Klaviyo account). - **Subscriptions** define _which_ events are routed to a connection. All resources are scoped to the authenticated user's organization. contact: name: Sendcloud API Support email: contact@sendcloud.com license: name: Apache 2.0 url: https://www.apache.org/licenses/LICENSE-2.0.html servers: - url: https://panel.sendcloud.sc/api/v3 description: Sendcloud Production security: [] tags: - name: Connections - name: Subscriptions - name: OAuth2 - name: Broadcast - name: Events paths: /event-subscriptions/connections/{id}/authorization: parameters: - schema: type: integer in: path name: id description: The id of the connection to authorize. required: true post: tags: - OAuth2 summary: Start OAuth2 authorization description: >- Initiate the OAuth2 authorization flow for a connection that requires it (e.g., Klaviyo). Returns an authorization URL to redirect the user to. operationId: sc-public-v3-scp-post-start_authorization responses: '200': description: OK content: application/json: schema: description: OAuth2 authorization URL type: object properties: data: $ref: '#/components/schemas/connection-authorization-response' examples: AuthorizationUrl: summary: OAuth2 authorization URL value: data: authorization_url: >- https://www.klaviyo.com/oauth/authorize?client_id=sendcloud&response_type=code&redirect_uri=https%3A%2F%2Fpanel.sendcloud.sc%2Fapi%2Fv3%2Fevent-subscriptions%2Fconnections%2Fauthorization%2Fcallback&state=abc123 '404': description: Not Found content: application/json: schema: $ref: '#/components/schemas/errors' security: - HTTPBasicAuth: [] - OAuth2ClientCreds: [] components: schemas: connection-authorization-response: title: Authorization Response description: >- Response containing the OAuth2 authorization URL for connecting external services like Klaviyo. type: object properties: authorization_url: type: string format: uri description: >- The URL to redirect the user to for OAuth2 authorization with the external service. errors: title: Errors type: object description: A standardized format for errors in JSON:API responses. properties: errors: type: - array - object items: type: object allOf: - $ref: '#/components/schemas/ErrorObject' required: - status - code - detail ErrorObject: title: Error type: object description: Error in a JSON:API error format properties: id: type: string description: A unique identifier for the error. links: type: object description: >- A set of hyperlinks that provide additional information about the error. properties: about: type: string description: A URL that provides additional information about the error. status: type: string format: int32 description: The HTTP status code of the error. minLength: 1 code: type: string description: A unique error code for the error, in snake case format. minLength: 1 enum: - unknown_field - invalid - forbidden - invalid_choice - min_value - 'null' - not_found - required - not_a_list - non_field_errors - authentication_failed - validation_error - parcel_announcement_error title: type: string description: A short, human-readable summary of the error. minLength: 1 detail: type: string description: A human-readable explanation of the error. minLength: 1 source: type: object description: >- An object that identifies the source of the error within the request payload. properties: pointer: type: string description: >- A `JSON` pointer to the location of the error within the request payload. parameter: type: string description: The name of the `query` parameter that caused the error. header: type: string description: The name of the `header` parameter that caused the error. meta: type: object description: Additional metadata about the error. securitySchemes: HTTPBasicAuth: type: http description: >- Basic Authentication using API key and secrets is currently the main authentication mechanism. scheme: basic OAuth2ClientCreds: type: oauth2 description: >- OAuth2 is a standardized protocol for authorization that allows users to share their private resources stored on one site with another site without having to provide their credentials. OAuth2 Client Credentials Grant workflow. This workflow is typically used for server-to-server interactions that require authorization to access specific resources. flows: clientCredentials: tokenUrl: https://account.sendcloud.com/oauth2/token/ scopes: api: Default OAuth scope required to access Sendcloud API. ````