> For the complete documentation index, see [llms.txt](https://docs.nexusglobalpayments.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nexusglobalpayments.org/payment-processing/payment-flow-happy-path/booking-flow-for-source-psps.md).

# Booking flow for Source PSPs

Nexus does not prescribe the internal booking flow for PSPs (ie how and when they should debit the Sender/Debtor Account). However, payments submitted to Nexus cannot be stopped or recalled, meaning that payments in error can only be recovered by manual communication between the Source PSP and Destination PSP. Therefore the Source PSP **should** always ensure the payment can be processed on the account **before** sending the transaction.

This results in the following options for the Source PSP:

**Option 1: Reservation followed by Booking**

* The Source PSP validates the payment and makes a funds reservation on the Sender’s account.
* The funds reservation must be upheld until the final response is received from the Source IPS.
* When the response indicates successful processing of the payment (an `ACCC` response), the funds reservation results in a debit booking on the Sender’s account.

**Option 2: Booking with optional reversal**

* The Source PSP can also opt for the option of debiting the Sender’s account before sending the instruction to the Source IPS for further processing.
  * If the response is received with an `ACCC` code, no further action is required.
  * In case the response indicates a `RJCT` code, the original debit on the Senders account must be reversed, resulting in a debit and credit booking.


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