> For the complete documentation index, see [llms.txt](https://docs.verifone.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.verifone.com/hardware-products/hardware/engage-devices/ux1-3-4xx-series/ux4xx/ux401-installation-guide/troubleshooting-guidelines.md).

# Troubleshooting Guidelines

This chapter lists possible malfunctions that may occur while operating a UX401 device and the appropriate corrective action. If the problem persists — even after performing the outlined guidelines — or if the problem is not described, contact your local Verifone representative for assistance.

{% hint style="info" %}
The unit comes equipped with tamper-evident labels. The reader contains no user-serviceable parts. Do not, under any circumstance, attempt to disassemble the unit. Perform only those adjustments or repairs specified in this guide. For all other services, contact your local Verifone service provider. Service conducted by parties other than authorized Verifone representatives may void any warranty.
{% endhint %}

## Transactions Fail to Process

If a contactless transaction fails to process:

* Perform a test transaction using one or more different contactless cards to ensure the problem is not a defective card.
* Ensure that you are conducting the contactless transaction properly (see [Using the Reader](/hardware-products/hardware/engage-devices/ux1-3-4xx-series/ux4xx/ux401-installation-guide/setup.md#using-the-reader)).
* Ensure that all cables and external power connections are connected properly to the contactless unit and all external devices (see [Connecting Unit to a Controlling Device](/hardware-products/hardware/engage-devices/ux1-3-4xx-series/ux4xx/ux401-installation-guide/setup.md#connecting-unit-to-a-controlling-device)).
* If the problem persists, contact your local Verifone representative.


---

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