"Your custom data has an invalid format." means that your application sent UserGuiding JS client a different data type than you've set in your dashboard.
To fix this, ensure you're tracking data in the same exact format you've set in your custom attribute.
There are 4 possible data types;
1-) Text
2-) Number
3-) Date
4-) True/False
Related Articles:
Creating Segments
What is Custom Attribute?
Creating Custom Attributes