> ## Documentation Index
> Fetch the complete documentation index at: https://docs.invoca.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Why Doesn't the Phone Number Swap With an Error About requiredParms and No PPCN?

> If "Parameters Required to Run" is enabled on your Tag, the number won't swap — and this error appears — unless that parameter is present in the visited URL.

If you've enabled the "Parameters Required to Run" setting in your Invoca Tag, the specified parameter must be present in the URL you're visiting for the number swap to occur. If that parameter is missing, an error appears when inspecting the webpage.

**Applies to:** Invoca Tag, Number Swap

## Where to go next

* [Configure the Invoca Tag to Selectively Swap for Paid Media Sources](/s/article/selectively-swap-paid-media)
* [Tag Deployment Troubleshooting: Duplicate Query Parameters in a Test URL](/s/article/tag-deployment-troubleshooting)