In principle, a termination via WhatsApp is legally valid. The law does not stipulate any special formal requirements for the termination of employment, which means that notice can also be given verbally or, as in the present case, by electronic transmission.
Attention I: If the employment contract provides for written notice of termination (i.e. with a handwritten signature), termination via WhatsApp would be invalid.
Attention II: The notice of termination must be received. If the receipt of the notice of termination is disputed, this can lead to difficulties in providing evidence. Employers should always obtain a receipt for a termination.