When a property value is underlined in red, it is invalid. A value is deemed invalid when:
The property value is not compatible with the property type (e.g., the contact has a text value in a date picker type property); or
The property value doesn't match any options in the property, when the property type is one of the enumeration types (i.e., a dropdown select, multiple checkboxes, radio select, or single checkbox).
Example scenarios that lead to an invalid value include:
A value was entered into the property, but the property is later changed to another type, making the original value invalid. For example, a value was entered in a Single-line text property but the property was changed to a Date picker type.
The contact has an invalid property value set via the Forms API. The Forms API allows any value to be passed to a property, even the value is invalid.
To fix an invalid error issue, you can:
Manually edit the value so that it is compatible with the property type (e.g. update the text value to a date value).