"I am telling you this one more time."

i am a native speaker, 'bunu sana bir kez daha söylüyorum' doğru bir çeviri

So 'Ben bunu sana' is an incorrect order? Is the correct sentence structure subject, object, indirect object?

Usually duolingo is very progressive and helps you understand what's going on, even without the grammar explanations (I'm using it 100% on android). This is why I use it and love it. But that sentence? Out of nowhere and immediately asking for full Turkish typing? No explanation on what I do wrong and the same exercise again and again until I write it the way it wants me to? Please enrich the possible translations for this one (various synonyms and word ordering options?) and place it elsewhere or at least introduce it more progressively in the lesson. Thanks a lot.