Restore Purchases button not working. – Quran Al Kareem القرآن الكريم Review

This is the most wonderful Quran app that I have been enjoying for past 2 years. I have paid for this app but restore purchase button not working on my new phone X. Please advise how to fix this issue
Review by Sam.Siddiqui on Quran Al Kareem القرآن الكريم.