Is there any impermissibility in inviting friends via WhatsApp to pray two rak'ahs on a specific night, with the intention of reminding them to pray, not to impose a Sunnah or innovate it, along with the phrase, "Pray two rak'ahs so that when Allah looks upon the earth, He sees people dancing and people praying beneath His Throne. Are you ready, my brothers in faith? Share it and you will be rewarded"?

Designating a specific act of worship to a particular time, or encouraging it without legitimate Shar’i evidence, is an innovation (bid‘ah). Examples include committing to fasting on the 15th of Sha’ban and performing night prayers on its eve. Therefore, it is feared that the message mentioned in the question might be an innovation. Instead, people can be reminded of the virtue of worship during times of heedlessness, without specifying a particular time.