apt - Unable to install postgresql-server through preseed

I am trying make unattended ubuntu-server-16.04.3 iso image. I have updated isolinux.cfg and txt.cfg to take the new preseed file. All I need is unattended ubuntu server with postgres server running.

Here is my seed file:
https://pastebin.com/xDpViuaw

I didn't add any new deb's. Same ISO image if tried manually, I can select postgresql server from option and I can easily complete it.

I have tried so many links and it always ended with below error as in attached image.
https://i.stack.imgur.com/xLvLl.png

If i remove postgresql from preseed file, i can complete the installation without any errors.

Can anyone point me how to resolve it?
Anything I am missing/doing wrong in preseed file?

PS: partitions are done as part of kickstart file