It's the whole second part of the sentence. I can't figure out what "advanced technology of/in transaction" means. I could make a few guesses, but it isn't in any way clear.
For example, the transaction being discussed. That could conceivably refer to the transaction of buying stamps or other items from the post office. It could refer to paying bills at the post office. It could refer to making other financial transactions, like purchasing money orders or the like.
All I can think is that it is saying that post offices have advanced technology in place to assist people with making transactions... of some sort! Or, it could mean that they have technology which allows people to make advanced transactions, whatever they may be. It's all a bit meaningless.
On the other hand, perhaps I'm just particularly dense today. Does it make sense to anyone else?