In the four-party payment model, what is a major feature?

The major feature of the four-party payment model being an allowance for an unlimited number of participants is fundamental to its structure. This model typically includes four key entities: the cardholder, the issuer, the merchant, and the acquirer. By its very design, this framework supports the inclusion of numerous issuers and acquirers, facilitating participation from a variety of financial institutions and merchants, which enhances the accessibility and versatility of the payment system. This open-ended nature allows for competition and innovation among providers, ultimately benefiting consumers and merchants alike.

The other options do not accurately capture the essence of the four-party payment model. For instance, a single organization operating the model contradicts the need for a diverse range of participants. Similarly, having issuers and acquirers as the same entity would limit the independence that is a hallmark of this model. Lastly, while network fees may be present, the statement that there are no network fees is not consistent with how the payment ecosystem functions, which often involves various costs associated with transactions.