  In this work, we implement the semi-analytical WKB method to explore the
behaviour of a scalar field on a traversable wormhole space--time with a
Casimir--like complexity reported in Eur. Phys. J. C 82, 420 (2022). We
estimate the error in the computation of the quasi--normal frequencies of the
scalar field at each order in the WKB and show that the order with the best
accuracy is not unique. We compute the value of the quasinormal frequencies for
the smallest estimated error. As an aside, we find that the imaginary part of
the quasinormal modes frequencies approach to zero for the fundamental mode
mimicking the so--called quasi--resonance observed for massive scalar fields in
the Reissner--Nordstr\"{o}m background.
