From the official website of WhatsApp you can read the FAQ in which the minimum requirement for KaiOS is version 2.5.1, but it is not so, we know it well! New versions of WhatsApp can be adapted for old firmware versions such as thecustom ROM GerdaOS (based on a v13 firmware for Nokia 8110 4G).

This guide should work for any version of WhatsApp downloadable from the KaiStore. For more devices and for old v12 and earlier, more apps wont work properly because the /system/kaios folder that contains the APIs needed. Often should be enough to change that. Learn more on the related extreme guide:

For the current state of off-the-shelf app, patching process is as follows [you need a stock-flashed phone with WA installed (for 8110 - with v15 and above), a target phone and adb]:

1) Gain the temporary root on the stock.

2) Create a directory and enter it, and then create another directory called application, for instance:

mkdir -p ~/wa-patch && cd ~/wa-patch && mkdir application

3) Pull the contents of the WA application already installed on the rooted stock:

adb pull /data/local/webapps/kaios.whatsapp.net/application.zip application/application.zip

4) Unpack the contents and remove the archive itself:

cd application && unzip application.zip && rm application.zip

5) Remove META-INF directory (this is very important, otherwise signatures will not match):

rm -rf META-INF

6) Find the line that looks like this in the page.js file (starts with if(!window.Intl)):

if(!window.Intl)throw f(856),new Error("os unsupported (Intl is missing)");

7) Replace this line with this:

if(!window.Intl)window.Intl=window.mozIntl;

Save the file.

7.1) (Optionally) remove the next statement after Intl-related (contains planned app expiration date) from the same page.js that looks like this:

if(Date.now()>=1569023999e3)throw f(414),new Error("expired app");

(in this case it's pointing to expire at September 21 2019)

Save the file.

8) If you want to, you may already deploy the patched version via old Firefox/PaleMoon/NewMoon WebIDE or XPCShell onto the target. If you wish to create the GerdaPkg/OmniSD-compatible package, proceed to the next step.

9) Staying within application directory, repack the application.zip:

zip -9r --exclude=*.git* --exclude=*.DS_Store* --exclude=README.md ../application.zip .

10) Go to the level above and create metadata.json:

cd .. && echo {\"version\": 1, \"manifestURL\": \"app://kaios.whatsapp.net/manifest.webapp\"} > metadata.json

11) Staying in the level above, pack the GerdaPkg package:

zip -9 whatsapp.gpkg.zip application.zip metadata.json

Now you can transfer, install and test the ready package (whatsapp.gpkg.zip) on the GerdaOS/v13 target.

1) Get a root access on your phone, for example using a temporary backdoor as it is showed in this forum;

2) Whatsapp messages are stored in the whatsapp directory placed in /data/local/storage/default;

3) Copy your whatsapp directory, which name is 1059+f+app+++kaios.whatsapp.net THE NUMBER AT THE BEGINNING IS VARIABLE;

4) Remove and reinstall the app;

5) Go back in the /data/local/storage/default folder, check what's the name of the new whatsapp installation (ex: 1073+f+app+++kaios.whatsapp.net) and then copy your backup in place of the new folder by changing its name.