Hello,
Can you please check what type of geometry was selected in Describe Geometry Task. It seems you have selected it as only solid with cap openinngs as yes, this won't work in this case.
You can either make your geometry hollow and go ahead with simillar approach or select geometry type as "only fluid region with no voids" with same model.
For detailed explaination on Watertight Geometry Workflow please refer following course
Mesh Generation using Ansys Fluent Meshing | Ansys Courses
Thanks,
Omkar