I didn’t have time to search for a source when I posted earlier, but here is a link from a few months ago explaining the fee.
Please note that I “misspoke”, above, on the fee for higher cashback amounts. The article breaks down the fees as this:
For amounts between $100 and $150, the fee will be $1.50. For $150.01 to $2,000 it will cost you $3.50. For amounts between $2,001 and $9,999 it will cost $6 to get your cash.