What is RockFlow fee?

Could you please clarify for me what exactly the RockFlow fee entails? I've heard it mentioned in the context of cryptocurrency transactions but I'm not entirely sure of its purpose or how it's calculated. Is it a flat rate, a percentage of the transaction value, or something else entirely? Additionally, does the fee vary depending on factors such as the type of transaction, the size of the transaction, or the time of day it's processed? I'd appreciate any insight you can provide on this matter.