Issue SP Access Token

Issues a short-lived SP Digital access token for the calling integration. Example curl: ``` bash curl --request POST '{{base_url}}/sp/auth/token' \ --header 'Content-Type: application/json' \ --data-raw '{ "client_id": "{{client_id}}", "client_secret": "{{client_secret}}" }' ``` Example success response shape: ``` json { "success": true, "message": "SP access token issued successfully.", "data": { "access_token": "<bearer-token>", "token_type": "Bearer", "expires_in": 7200, "expires_at": "2026-04-06 14:30:00", "scope": "wa.members.read wa.members.write wa.wallet.read", "business_id": 2, "integration_id": 1 }, "meta": {} } ``` Example error response shape: ``` json { "success": false, "message": "The provided SP client credentials are invalid.", "error": { "code": "invalid_client_credentials", "details": {} } } ``` Notes: - Access tokens expire after 2 hours. - No refresh token is issued in this flow. When the token expires, call this endpoint again with the same `client_id` and `client_secret`.