Setting cash advance to zero does not help. Cash advance is typically 3%.

Some bank categorize Plastiq as cash equivalent which has a flat 5% fee. You get hit twice because Plastiq payments are two transactions. If you pay say $500 using Plastiq and if the bank considers as cash equivalent then

$500 will result in $25 fee from the bank
Plastiq fee $ 12.5 will result into additional $10 fee (Minimum fee)

So there is a possibility of paying $35 fee to the bank over and above $12.5 one pays to Plastiq.