Inspired by Lie algebra expansion, we consider an extension of the introduced in A. Fontanella and S. J. van Tongeren [Coset space actions for nonrelativistic strings, High Energy Phys. 06 (2022) 80.] string coset action ${\mathrm{AdS}}_{5}\ifmmode\times\else\texttimes\fi{}{\mathrm{S}}^{5}$. We show that extended admits a nondegenerate inner product which is adjoint invariant under full algebra...