Because our wrong estimate (we estimated all the goods is about 60Kgs in total, you can find attached e-mail records)
but the actual weight is about 113kgs (you can find attached PACKING LIST).
About the air freight:
Actual air freight = USD 412
You've paid us = USD 310
You still should pay us = USD 100
So could you pls pay this USD 100 together with our next order ?