You have to register your postnup where your marriage has been registered. If the marriage was muslim, in KUA. If the marriage was non-muslim or it was abroad, it should be registered in Catatan Sipil. Courts do not register contracts anymore and stopped decades ago, and they would refuse to do so if you ask them to do a contract registration.
Ok, then it is still as I thought and as I was told by our notary. Married abroad, so only registration at cat. sipil needed.