WhatsApp for Samsung Galaxy C9 Pro

The C9 Pro shipped with Android 6/7 and is long past Samsung support, so newer WhatsApp builds eventually drop support for it. As a stopgap, keep your chats backed up often (in WhatsApp go to Settings > Chats > Chat backup and back up to Google Drive), but the lasting fix is moving to a current phone or flashing a community ROM that raises the Android version. If you retire the phone, the installed WhatsApp version may keep running for a while, but migrate before the cutoff so you don't lose access. See how others solved this on Reddit

This is usually the proximity sensor thinking the phone is at your ear, so audio routes to the earpiece instead of the loudspeaker. Wipe the top of the screen near the front camera and earpiece (a case or screen protector can cover the sensor), then play the voice note while holding the phone away from your face. Also confirm media volume is turned up and that the phone isn't connected to a Bluetooth speaker or car system that is silently grabbing the audio under Settings > Connections > Bluetooth. A quick restart often clears a stuck sensor. See how others solved this on Reddit

Restore only works when the same Google account that holds the Drive backup is signed in on the phone and you verify the identical phone number. Add that Google account first under Settings > Accounts and backup > Manage accounts, then during WhatsApp setup enter your number and tap Restore when prompted. If you turned on end-to-end encrypted backup, you must enter that password or 64-digit key, or the backup stays locked. Without the matching account, phone number, and encryption key there is no way to decrypt it. See how others solved this on Reddit

WhatsApp uses each person's full international number including country code, and it automatically finds anyone in your phone contacts who also uses WhatsApp - there is no separate friend list. Save new people in Contacts with the + and country code (for example +1 for the US), then open WhatsApp and tap the new-chat icon to pick them from the contact list. If someone doesn't appear, re-check that their saved number includes the correct country code and that they actually have WhatsApp installed. See how others solved this on Reddit

There is no official LineageOS build for the C9 Pro, so you'd rely on an unofficial port - that means unlocking the bootloader, installing a custom recovery, and wiping the device, so back up WhatsApp to Google Drive first. A newer Android base can restore WhatsApp compatibility, but expect some features (camera, sensors) to be flaky and Play Integrity / safety checks to break. Only attempt it if you accept the risk of bricking the phone; for most owners, moving to a supported phone is the safer route. See how others solved this on Reddit

Custom ROMs fail Google's Play Integrity check, so banking and some other apps refuse to run even when WhatsApp itself works. The common workaround is rooting with Magisk and adding a Play Integrity Fix module so the device passes the basic integrity check, but strong integrity (used by stricter banking apps) often can't be satisfied on an unofficial ROM. If those apps are essential, the most reliable fix is flashing back the official Samsung firmware so the device passes integrity natively. See how others solved this on Reddit