This is incorrect . The system is not P2P, while it appears to be for customers. The BCB keeps both the directory that ties a chave pix to an actual account (DICT), and a centralized ledger (SPI - Sistema de pagamentos instantaneo)

[Payer bank] ──(1. Lookup key)──> [ DICT - Name Service] (Returns account data)

         │

  (2. Send order)

         ▼

     [ SPI - Central Ledger] ──────(3. Real time settlement over Financial Institutions account: Debt/Credit)

         │

  (4. Notification Message)

         ▼

[Receiver Bank]

The ledger doesn't keep individual accounts, but a Instant Payments account for each institution. This account is not the master bank account in the Reserve Transfer System (Sistema de Transferencia de Reservas) which is the system of record for banks funds, so the banks need to allocate funds from the STR to the SPI every day to be able to honor PIX transfers. The STR system doesn't work out of normal banking hours, so the banks need to predict how much money they will need for PIX transfers and move that money from the STR to the PI (pagamento instantaneo) account during defined liquidity transfer windows, to avoid banks double-spending the same funds over different rails (traditional vs PIX). If a bank finds itself without funds on its PI account in a saturday night, it can loan the funds from another bank who still have excess liquidity on his PI account).

As you can see, between the SPI, STR an DICT, it is a very centralized system.

Also, the system operates in a dedicated zero-trust networks which is completely isolated from the internet. The messages between banks and the central bank follow the ISO 20022 format. IBM MQ is used to route messages back and forth between banks and the BCB.