There is no significance as this is not from the sunnah!

Please what is the basis of closing one’s du’a (supplication) by saying “Subhana Rabbika Rabbil Izzati Amma Yasifoon, Was-Salamun Alal Mursalin, Walhamdu Lillahi Rabbil ‘Alamin.” (the last 3 verses of Suratul Saffat) & is it fine to do so?

Supplications |