> For the complete documentation index, see [llms.txt](https://emotiv.gitbook.io/flex-2.0-user-manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://emotiv.gitbook.io/flex-2.0-user-manual/support/troubleshooting.md).

# Troubleshooting

### Unable to Achieve Contact Quality on Any Channel

There could be two reasons for this happening:

1. The sensor trees are not plugged into the FLEX controller; or
2. The reference sensors are not connected to your participant. Please make sure there is contact with both DRL and CMS. 

### The Input Channel is Always Black

There could be two reasons for this happening:

1. There is no contact quality (see above); or
2. There could be an error with your FLEX Controller. If this is the case, please contact [EMOTIV Support](https://www.emotiv.com/contact-support/).