Tamilvanan, KAlkhaldi, AJakhar, JChugh, RJakhar, J2024-10-152024-10-152023-01http://hdl.handle.net/123456789/1734In this work, we investigate the refined stability of the additive, quartic, and quintic func tional equations in modular spaces with and without the ∆2-condition using the direct method (Hyers method). We also examine Ulam stability in 2-Banach space using the direct method. Additionally, using a suitable counterexample, we eventually demonstrate that the stability of these equations fails in a certain case.