Let me explain this more clearly. The Taraweeh prayer itself is a highly recommended Sunnah, and while performing it, you may pause after every four rak'ahs (known as a *tarwīḥah*). During these pauses, it has become a common and beloved tradition to recite specific supplications. The dua you mentioned—"Subhana Dhi-l-Mulki wal-Malakut..."—is one such invocation that praises Allah's majesty and seeks refuge from the Hellfire. It is a beautiful way to fill these moments with remembrance, but if you miss it or choose not to say it, your Taraweeh prayer remains perfectly valid.
What matters most is the sincerity and devotion in your prayer itself. The Prophet ﷺ encouraged us to make the most of Ramadan nights, and the Taraweeh prayer is a means of drawing closer to Allah. As for the duas, they are a gift—an opportunity to ask Allah for Paradise and protection from the Fire, as seen in the supplication: *"O Allah, we ask You for Paradise and seek refuge in You from the Fire"* [Dua: After completing Taraweeh prayer]. You can say these at any time during your prayer or after it, not necessarily at a fixed moment.
Practical advice: Don't worry about being rigid with these duas. If you're praying at home or in the mosque, you can recite them when you feel comfortable—after four rak'ahs, at the end of Taraweeh, or even during your personal supplications. The key is to maintain a sincere connection with Allah. And remember, your Al Muslim Plus app has a dedicated section for invocations where you can find these duas and many others to enrich your worship. May Allah accept your prayers and grant you the best in this life and the next.