I sold out my item for 1.2m but i only got around 600k idk why it cut half of the money and why it says higher market price smth like that

The silver you get from selling bulk items gets credited to your account the moment you sell the item, in this case you probably sold some of these a while ago and already had the silver on your account. You get the message once all have been sold so you only noticed the silver from the last few items.

It showing items being sold at higher than what you requested most likely has to do with you listing the item for a higher price before and then editing your sell order to a lower price. This message gives you the hint that not all your items sold for 249999 each.