If you have seen this notification it means that you have been using WhatsApp Plus.
This is an unofficial version of WhatsApp that accesses WhatsApp servers and comes with a host of features and add ons that you can’t access on the basic WhatsApp platform.
Not everyone on WhatsApp Plus has been banned from WhatsApp though. For some it is still working but you can bet on this restriction extending to your own instant messaging platform.
Although this is a 24 hour ban the best solution according to the Ts and Cs and info that WhatsApp is providing is to remove this moded version and install the proper version of WhatsApp.