You cannot always unsend or edit messages on iMessage due to several factors:

  1. Compatibility: These features require both sender and receiver to be using devices with specific operating systems:

    • iOS 16 or later
    • iPadOS 16.1 or later
    • macOS 13 or later

    If either party uses an earlier OS version or non-compatible platforms such as SMS, the functionality may not work correctly.

  2. Time Limitations: There are strict time constraints for each operation:

    • Unsending a message is possible within 2 minutes of sending.
    • Editing a message can be performed within 15 minutes of sending, limited to 5 edits per message.
  3. User Experience Issues: Some users reported losing the ability to unsend or edit messages without clear reasons, though this could be related to temporary glitches or system issues.

Please keep in mind that if the recipient doesn't meet the compatibility requirements mentioned above, the original message will remain visible despite attempts to unsend or edit it.