WhatsApp is probably the most used messaging service across all platforms. It is probably one of the most secured platforms for texting available for it does not store any texts on their servers as per reports. Moreover, only one WhatsApp can be used per device, as every account is associated with only one address. This makes it very useful and safe as no one can else your phone number to get an account in your name. In addition, each time you log in to your WhatsApp account you need to verify it with a password sent to your number used at the time of sign-up. In other words using same WhatsApp account for two devices is logically not possible.
However if you face a problem and you are stuck using your phone, you can use the WhatsApp web feature to cast your WhatsApp screen using the phone’s internet. For this to work if you need to have both the devices are on same network and have the phone you use for WhatsApp. It is only legit and legal way you can use same WhatsApp on another device without violating any policy.
Steps To Use Your WhatsApp on Other Device
These simple steps can help you use your same WhatsApp on other device.
Open your WhatsApp
Open your WhatsApp account on the phone you are already logged into. This method will not work if you have logged out of your account or have no access to your phone. Moreover, you have to make sure your other phone is connected to the internet of your primary device.
Open Menu

Click on the 3 dots on the top right corner to access the menu option.
Choose WhatsApp Web

In the settings menu, chose ‘WhatsApp Web’ and it will show all the devices you are logged into. If you want to add a new device, select the + sign, it will open a window with a scanner.
Visit web.whatsapp.com
On the device, you want to cast the screen or use your WhatsApp, open the browser and type ‘web.whatsapp.com’. It will show a QR code on the screen
Scan the code to connect

Scan the QR code on the other device using the scanner window mentioned in Step 3. It will automatically connect to the other device, it will prompt to save the device and continue.
Now you can see your WhatsApp screen on the other device as use it as your normal WhatsApp. It is a very handy feature to use if your phone is causing trouble but cannot afford to create a new account. Works as your usual WhatsApp until both devices are connected to each other. It uses your phones internet to connect so make sure your phone has an active internet connection.