> For the complete documentation index, see [llms.txt](https://docs.aurelia.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.aurelia.io/developer-guides/error-messages/4100-to-4106/aur4108.md).

# AUR4108

## Error Message

`AUR4108: GroupRule execution result is invalid.`

## Description

This error occurs when a `GroupRule` returns an unexpected result shape from execution (for example, missing expected fields or returning a non-boolean/non-result type where a result is required).

## Example Trigger

This is most often caused by a custom rule implementation returning an invalid value.

## Solution

* Ensure custom/group rule implementations return the expected validation result type.
* If a rule is async, return a `Promise` that resolves to a valid result.

## Troubleshooting

* Log the value returned by the failing rule to see what is being produced.
* Review custom rules for correct return types and error handling.


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