WhatsApp for Vivo V40

Vivo's Funtouch OS aggressively kills background apps to save battery, so WhatsApp only delivers messages when you open it. Fix it with a few settings: go to Settings > Battery > High background power consumption (also called Background power consumption management) and allow WhatsApp; open Settings > Apps & permissions > Autostart and enable WhatsApp so it can wake itself; and in Settings > Apps & permissions > App manager > WhatsApp > Battery, set it to allow background activity and turn off any sleep/optimization. Finally, lock WhatsApp in the Recent apps screen (swipe the card down or tap the lock icon) so the system stops clearing it. Keeping 'Stay connected when sleeping' on under Settings > Battery > More settings prevents the connection dropping overnight. See how others solved this on Reddit

First confirm the number is entered with the correct country code and that the SIM can receive a normal SMS from another phone. If the code still won't arrive, let the timer run out fully and choose 'Call me' for a voice OTP instead, and make sure WhatsApp has SMS and Phone permissions under Settings > Apps & permissions > Permission manager. A weak signal or a fresh/ported SIM can delay codes for hours, so toggling Airplane mode or trying on Wi-Fi often helps the code come through. See how others solved this on Reddit

Open Settings > Apps & permissions > Permission manager > Microphone and confirm WhatsApp is set to 'Allow', since a denied or 'ask every time' setting cuts out audio. If the permission is fine, clear WhatsApp's cache via Settings > Apps & permissions > App manager > WhatsApp > Storage, and check that no other app (recorder, dialer) is holding the mic. Removing any screen protector film over the bottom mic hole and testing in the phone's Recorder app helps confirm whether it's a hardware issue. See how others solved this on Reddit

Grant both Camera and Microphone to WhatsApp under Settings > Apps & permissions > Permission manager, and make sure mobile data and Wi-Fi are both allowed for WhatsApp under Settings > Apps & permissions > App manager > WhatsApp > Data usage. Disable battery optimization for WhatsApp so the OS doesn't throttle the call, and test on a different network, since a restrictive Wi-Fi or weak signal is the most common cause of dropped video calls. Updating WhatsApp from the Play Store rules out a buggy build. See how others solved this on Reddit

If you're moving from another Android phone, back up on the old device first via WhatsApp > Settings > Chats > Chat backup to Google Drive using the same Google account, then sign in with that account on the V40 and restore when prompted during setup. Coming from an iPhone, use WhatsApp's official 'Move to Android' tool with a USB-C cable, since iCloud backups can't be read directly by Android. Always use the same phone number, and keep both phones charged and on Wi-Fi throughout the transfer. See how others solved this on Reddit