Error states for the Rebar Coupler 
   Namespace:   Autodesk.Revit.DB.Structure  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 17.0.0.0 (17.0.1090.0) 
Syntax
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Members
| Member name | Description | 
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| ValidationSuccessfuly | Bars can be coupled | 
| IncorrectInputData | Cannot place rebar coupler. | 
| DifferentLayout | The rebar sets have different numbers of bars. | 
| BarsNotTouching | The selected ends of the bars are too far apart. | 
| IncorrectEndTreatmentHook | The coupler cannot be placed at an end that already has a hook. | 
| IncorrectEndTreatmentCoupler | The coupler cannot be placed at an end that already has a coupler. | 
| BarSegementsAreNotParallel | The selected legs are not aligned. | 
| BarSegmentsAreNotOnSameLine | The selected legs are not aligned. | 
| InconsistentShape | One of the selected bars has an incorrect shape. | 
| InvalidDiameter | The selected coupler type cannot be applied to the selected bar size(s). | 
| CurvesOtherThanLine | Cannot place rebar couplers on circular legs. | 
| BarSegmentSmallerThanEngagement | The selected leg is shorter than the bar engagement. | 
| VaryingDistanceBetweenDistributionsBars | All the bars from the selected sets, which need to be connected, must be separated by the same distance. |