Hi,
If I understand correctly how this xTras command works, you need to define your manifold as
DefManifold[Mdim, dim, {α,β,γ,δ,μ,ν,λ,σ,ζ,χ,τ,ω}]
using the constant symbol dim defined by xTras, and then choose a value (say dim = 4) before doing the ConstructDDIs computation. If the dimension you choose is large enough, then you will not get any DDI.
Cheers,
Jose.