Card-not-present (CNP) transactions — online payments, keyed-in over the phone, or invoiced — carry higher interchange than card-present transactions because the fraud risk is higher. A typical CNP rate is 30–50 basis points more than the same card swiped chip-in-person.
This is real interchange, not a processor markup. Even a perfectly-priced interchange-plus account will see CNP rates above CP rates. The fix isn't to eliminate the surcharge (you can't); it's to optimize each CNP transaction with full AVS verification, CVV, and 3D Secure to qualify for the lowest CNP tier.