Hi there! I see you're encountering a "transaction number expired" message in the POSTIDENT app. To help you better, could you tell me when you received that transaction number and how long ago you tried to use it? Usually, these transaction numbers (or case IDs) have a limited validity period.

In the meantime, here’s what you can do to resolve it:

1. Get a new transaction number: The transaction number expires after some time for security reasons. You'll need to initiate the identification process again to receive a fresh transaction number. This is typically done by the company or service that issued it to you.

2. Restart the identification process: Open the POSTIDENT app on your Android device, and enter the new case ID or scan the new QR code provided.

3. Check the validity period: Make sure to use the transaction number within the valid time frame to avoid expiry. The app guides you through the process and will highlight timing constraints.

If you’re unsure how to obtain a new transaction number, please let me know who issued your current one (for example, a bank or governmental agency), and I can guide you on the next steps or provide contact info.

Would you like me to walk you through requesting a new transaction number based on your situation?