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In this paper, we study the generalized Hyers–Ulam stability of Euler–Lagrange-type cubic functional equation of the form $$\begin{aligned} 2mf(x + my) + 2f(mx - y) = (m^3 + m)[f(x+ y) + f(x - y)] + 2(m^4 - 1)f(y) \end{aligned}$$ 2 m f ( x + m y ) + 2 f ( m x - y ) = ( m 3 + m ) [ f ( x + y ) + f ( x - y ) ] + 2 ( m 4 - 1 ) f ( y ) for all $$x,y \in X$$ x , y ∈ X , where m is a fixed scalar such that $$m \ne 0,1$$ m ≠ 0 , 1 , and f is a map from a quasi-normed space X to a quasi-Banach space Y over the same field with X by applying the alternative fixed point theorem.

Stability of Euler–Lagrange-Type Cubic Functional Equations in Quasi-Banach Spaces