> 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/investigation-and-enquiry/source-ipso-to-nexus.md).

# Source IPSO to Nexus

This leg covers the failure scenarios in the submission of the pacs.008 by the Source IPSO to the Nexus Gateway.

![](/files/X4usQqDldwAgCYiSgtEF)

The Source PSP must receive a technical acknowledgement (HTTP202) from Nexus to indicate a successful delivery of the payment to the Nexus Gateway. In the event the Source PSP does not receive this acknowledgement or receives a retry-able response (for example an HTTP429 - rate limit exceeded), the Source PSP should retry according to the Nexus retry mechanism.

**Source IPSO investigation process**

In the event the Source PSP has successfully sent the payment to Nexus but has not received a Payment Status Report (pacs.002), the Source PSP must initiate an investigation process. The Source PSP must send an Investigation Message (pacs.028). 

<figure><img src="/files/L4iSqlWMN3KvtN6ZIdbn" alt=""><figcaption></figcaption></figure>

Nexus will respond to the POST pacs.028 API with a Payment Status Report (pacs.002), containing the latest status of the transaction as known by Nexus. This can be used by the Source IPSO to complete its process. End-of-day, Nexus will also provide a camt.054 report containing the final and pending transactions.

The Source PSP **must not** unilaterally cancel the transaction. It must retrieve the final status of the transaction from Nexus.