What is KIP-9 and why can it raise my Kaspa fee unexpectedly?

KIP-9 is a Kaspa protocol rule that can require a higher fee even when the network is not congested. The KIP-9 mass constraints limit how much data a transaction can contribute to a block relative to the fees it pays; if your transaction is data-heavy — for example because it combines many UTXOs — you must pay more to satisfy this constraint regardless of current network load. This matters because it means your fee is not purely a function of how busy the network is: the structure of your own transaction can also push your required fee above the standard minimum.