To fix the issue where a pass added to your iPhone's Wallet app is not showing up in the Wallet app on your Apple Watch, you can follow these steps:
Make sure both devices are connected: Your iPhone and Apple Watch should be connected via Bluetooth. You can check this by opening the "Watch" app on your iPhone and ensuring that your watch is connected.
Update your devices: Ensure that both your iPhone and Apple Watch are running the latest version of iOS and watchOS, respectively. You can update your iPhone by going to Settings > General > Software Update, and your Apple Watch by going to the Watch app on your iPhone > General > Software Update.
Check Wallet app settings: Open the "Watch" app on your iPhone, tap the "My Watch" tab, scroll down, and tap on "Wallet & Apple Pay." Make sure "Mirror my iPhone" is enabled. This setting ensures that your passes are automatically synced between your iPhone and Apple Watch.
Make sure your Apple Watch is logged in to your Apple ID. You can check this by boing to the Watch app on your iPhone > General > Apple ID.
After confirming all these steps please remove the pass from your iPhone Wallet and try adding it again and confirm that it is also showing on your Apple Watch wallet.