Two payment networks, two cost models
Most B2B payments move on one of two networks: the bank-to-bank rails (ACH for batched payments, RTP for real-time), or the card networks (Visa, Mastercard, Amex). They look the same from the buyer's side (money leaves your account, lands in the vendor's account), but the cost structure underneath is very different.
Bank rails charge a per-transaction fee, typically a few cents to a few dollars depending on the bank and the volume. The fee is the same whether the payment is $100 or $100,000. It's the cost of the bank processing the transaction, and nothing more.
Card networks charge a percentage of the transaction (the interchange fee) usually somewhere between 2% and 4% of the total. On a $10,000 vendor payment, that's $200 to $400 in fees, every time. The percentage doesn't scale down for larger amounts; it scales up.
Where the interchange fee actually goes
Card interchange is split between several parties: the card-issuing bank, the network (Visa or Mastercard), the merchant's payment processor, and the merchant's own bank. The percentage covers fraud risk, rewards programs, chargeback protection, and the operating costs of the networks themselves.
For consumer card payments, where transactions are small and fraud risk is real, this model makes sense. The cost is bundled into the convenience of swiping a card. For B2B payments, the math is harder to defend. The fraud risk on a known vendor relationship is lower than on a consumer transaction. The rewards program doesn't really apply. The chargeback rights are limited. And the dollar amounts are large enough that the percentage adds up to real money fast.
Why this still happens
A lot of B2B card volume exists because it's the path of least resistance. The vendor takes a card because they want to get paid quickly; the buyer uses a card because the AP tool defaults to it; the rewards on a corporate card give the AP team some reason to prefer it; the cost gets absorbed somewhere on the vendor's side. Nobody is making the cost decision actively. It's just the inertia of how the AP function evolved.
Meanwhile, the bank rails got significantly better. Same-day ACH is now standard. RTP gives 24/7 instant settlement on transactions up to $10 million, with the limit rising over time. The infrastructure exists; it's just not the default in most AP tools.
What this means for finance teams
If you're paying vendors on cards primarily, the question worth asking is whether anyone has done the math on what the interchange is costing, across all your vendor payments, in a year. For a mid-market company with meaningful AP volume, it's typically a six-figure number. Often more.
Moving vendor payments to bank rails (ACH for routine payments, RTP for time-sensitive ones) is straightforward once the workflow supports it. The savings come from cutting interchange. The speed comes from RTP being faster than card settlement for the vendor. The audit trail comes from bank rails being directly tied to the bank's settlement record rather than reconstructed from card processor reports.
PayShore is built around the bank rails for this reason. The orchestration layer, the controls, and the approval workflows all sit on top of ACH and RTP, where the per-transaction cost is small and the path to the vendor is direct. The interchange savings aren't a feature; they're a consequence of building on the right infrastructure.