In short, i set the fee to 0.00099BTC/KB, but one of my transaction fees is only 0.00019182BTC/KB.
So, anyone knows what happened or what should i do to prevent that for future transaction? Also, can i set tx fee manually for each transaction?
TX ID : 5028d650536fa01003635f475c7feaf122abe4bc46e787cd44e05329d1fe0be7
I'm not sure why the fee wasn't to what you specified for this transaction. You didn't also specify a manual fee that overwrote the default fee did you?
Yes, Electrum has a spot to specify the fee manually for each transaction. However, you can't specify the per byte/KB fee individually for each transaction.
Personally, I'd recommend you use the Dynamic Fees feature ( Enable it in Preferences ) as this is better at estimating appropriate fees. It gives you a slider to control how soon you want the transaction to confirm and adjust the fees automatically. I've started using this rather than manual fees and it simplifies the process so much.