Viber on PC not syncing? Here is the solution.

I've noticed that Viber on my Ubuntu PC stopped syncing messages with Viber app on my mobile phone. I didn't find solution on Viber Help pages so I had to find the fix myself. It's actually very simple: you just have to delete one file and restart the application, no Viber reinstall is needed!

Before everything, exit Viber application on PC.

Let's find all Viber files and directories:

$ sudo find / -name "*viber*"
/var/lib/dpkg/info/viber.md5sums
/var/lib/dpkg/info/viber.list
/var/lib/dpkg/info/viber.postinst
/var/lib/dpkg/info/viber.prerm
/var/lib/dpkg/info/viber.preinst
/var/lib/dpkg/info/viber.0
/var/lib/dpkg/info/viber.copyright
/home/bojan/Downloads/viber.deb
/home/bojan/.cache/gnome-software/icons/4759200235b7bb401072b357b6bcd10db4e6c4a1-viber-icon-logo-4E5ED1327A-seeklogo.com.png
/home/bojan/.ViberPC/440123456789/viber.db-shm
/home/bojan/.ViberPC/440123456789/viber.db-wal
/home/bojan/.ViberPC/440123456789/viber.db
/usr/share/applications/viber.desktop
/usr/share/pixmaps/viber.png
/usr/share/viber
/opt/viber

NOTE: 440123456789 is the number of the mobile device to which you've been syncing messages so far.

/home/bojan/.ViberPC/440123456789/viber.db is file which contains all message history. Let's delete it: 

$ rm ~/.ViberPC/440123456789/viber.db 

Open Viber app on mobile phone and re-launch Viber on PC (from Applications or from Terminal, like here):

$ /opt/viber/Viber 

Attribute Qt::AA_ShareOpenGLContexts must be set before QCoreApplication is created.

qml: *** popupMode = 1920

qrc:/QML/DebugMenu.qml:262: TypeError: Cannot call method 'isWasabiEnabled' of undefined

qrc:/QML/DebugMenu.qml:289: TypeError: Cannot call method 'isSearchInCommunitiesForceEnabled' of undefined

qrc:/QML/DebugMenu.qml:296: TypeError: Cannot call method 'isOOABURISpamCheckerForceEnabled' of undefined

qrc:/QML/DebugMenu.qml:304: TypeError: Cannot call method 'isRateCallQualityForceEnabled' of undefined

We'll see prompts telling us to approve syncing on both PC and mobile applications:

Viber sync approval prompt on PC

Viber sync approval prompt on mobile phone

Viber sync start prompt on PC

After we approve syncing on both devices, syncing process will start:

Viber syncing message on mobile phone

Viber syncing message on PC

After the process completes your Viber on PC will be synced with mobile phone Viber app.

If removing viber.db does not help, delete also data.db:

 $ rm ~/.ViberPC/440123456789/data.db 

...and repeat the whole process.