Non ho trovato molti riscontri.

https://infinicept.com/payment-facilitator/learn/get-started...
https://www.lawinsider.com/dictionary/sub-merchant
https://www.quora.com/What-are-merchant-and-submerchant
https://www.google.com/search?q="sub commerciante"&rlz=1C1ON...
https://www.google.com/search?q="sub negoziante"&rlz=1C1ONGR...

‘Platforms using a traditional payfac solution open a merchant bank account and receive a merchant ID (MID) to acquire and aggregate payments for a group of smaller merchants, typically called sub-merchants. Traditional payfacs have embedded payment systems and register their master MID with an acquiring bank. Sub-merchants, on the other hand, are not required to register their unique MIDs; instead, transactions are aggregated under the payfac’s master MID. This is meant to reduce the complexity that sub-merchants would face when setting up online payments on their own since it eliminates the need for them to establish and maintain relationships with an acquiring bank, payment gateway, and other service providers.’


This extract was taken from a webpage in the Stripe website. Sub-merchants typically proliferate in an e-commerce environment.

qui, e altrove, si parla di merchant e sub-merchant
non lo tradurrei

Dall'altro lato, contribuiamo preoccupandoci della conformità con i merchant e i sub-merchant del marketplace
https://www.multisafepay.com/it_it/blog/i-tre-trend-piu-impo...

In questa fase, Stripe funge da commerciante (con il proprietario dell’azienda come sub commerciante). www.mercatinodigitale.it/come-funzionano-i-pagamenti-stripe

"esborsi dall'account del commerciante, transazioni contestate e modifiche allo stato dell'account sub-commerciante." ecommerce-platforms.com/it/ecommerce-reviews/braintree-payments-review

"indirizza automaticamente i fondi a commercianti e sub-commercianti il ​​giorno lavorativo successivo." cryptodnes.bg/it/ryft-poluchi-fca-licenz-stremi-atakuva-sektora-plashtaniqta/

sub-merchant invece qui non viene tradotto: https://www.pwc.com/it/it/industries/fintech/docs/fintech-bi...