Not able to select masks for registration in elastix

Operating system: Windows10
Slicer version: 5.6.2
Expected behavior: Registration between 2 abdominal CT image with masks
Actual behavior:
After import my binary mask as segmentations in slicer, I was not able to find a mask to select, as the following image shows:

Mask must be a label volume or segmentation. You can either convert the scalar volume to labelmap volume in Volumes module; or when you select the data for loading in the “Add data” window, choose “Segmentation” in Description column, or keep the description “Volume” and check the “LabelMap” option.

Thank you for your prompt reply, but I think I have imported my binary mask as segmentation:

But still, I am unable to select it from the masks in the elastix module.