This is a fake message. There are no government orders on GST being imposed on Whatsapp messages.
In March 2018, an image of the clipping of a newspaper article was circulated in social media. It stated that the Government of India would impose 18% Goods and Service Tax (GST) on sending and forwarding good morning messages on WhatsApp from the following month.
It was found that the article was from Navbharat Times' March 2, 2018, Delhi edition. The story carried the advisory 'Bura na mano Holi hai!' (Do not feel bad since it is Holi.), implying that the article was published in jest by the media organisation on the occasion of Holi.