What is the Vantiv fee?

Could you please elaborate on what exactly the Vantiv fee is? Is it a specific type of transaction fee charged by Vantiv, a financial technology company? If so, under what circumstances would this fee be incurred? Is it a flat rate or does it vary based on the amount of the transaction? Additionally, are there any ways to avoid or reduce this fee? I'm interested in understanding the ins and outs of this particular fee as it relates to cryptocurrency and financial transactions.