What a lovely use of a non defining relative clause! If this is for an exam and you want to show off your beautiful long sentence then it looks perfect (add in the changes that Nicholas has mentioned though!) But if you're sending this to a business contact or customer I recommend splitting it into two separate sentences to make it clearer. "Make the payment only when the book arrives in Singapore. The book is expected to arrive at Singapore port on 30/8/2017."

Make the payment only when the book arrives in Singapore, which is expected at Singapore port on 30/8/2017. -------- Here is the corrected sentence.