I've noticed an inconsistency in the page_id prefix of the post_id returned when publishing photos using the POST /v17.0/page-id/photos endpoint.

Expected behavior: The post_id should start with the page_id we use in the API, following the format: {page_id}_{post_id}

Current behavior: The returned post_id starts with a different page_id prefix than the one we use in the API. While this prefix is valid and corresponds to the same Facebook page, it differs from the page_id we typically work with across the Facebook API.

Important note: When fetching the same post later using GET /v17.0/me/posts endpoint, the post_id is formatted with the expected page_id prefix that we use in the API. This suggests the issue is specifically with the response format of the POST photos endpoint.

Examples: API Page ID: 123456789

When creating the post - POST /v17.0/page-id/photos: Response (unexpected prefix): { "id": "112233", "post_id": "987654789_123456" }

When fetching the same post - GET /v17.0/me/posts: Response (expected prefix): { "id": "123456789_123456" }

This inconsistency makes it difficult to maintain a standardized post ID format in our application and requires additional handling to ensure consistent post ID formats across our system.

Could you please investigate this behavior and explain why different page_id prefixes are used?

Thank you for your help.