What is the simplex transaction fee?

Can you please clarify for me what exactly is the simplex transaction fee? I'm curious to know if this fee applies to all transactions made using Simplex, or if it's specific to certain types of transactions. Additionally, I'm wondering if the fee is a flat rate or if it varies depending on the amount of the transaction. It would also be helpful to know if there are any ways to reduce or avoid this fee altogether. Can you provide me with more details on the simplex transaction fee?