To fix you need to build a version of your project in 5.5 or whatever is current at the time of reading this.
Unreal Marketplace Guidelines:
1.4.2.b Upon initial submission and approval, every product must contain a Project Version that has the latest version of Unreal Engine as a Supported Engine Version.
4.2.2.b Upon initial submission and approval, every product must contain a Project Version that has the latest version of Unreal Engine as a Supported Engine Version.