Compiler Error CS8802
Only one compilation unit can have top-level statements.
This error indicates that there are two or more top-level statements in a single compilation unit (single project or a single group of files compiled into a single binary file).
Example
The following sample of single compilation unit generates CS8802:
<!-- SingleCompilationUnit.csproj -->
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net8.0</TargetFramework>
</PropertyGroup>
</Project>
// EntryFile.cs
int a = 0;
// SecondaryEntryFile.cs
int b = 1; // CS8802: The top level statement already exists in EntryFile.cs
To correct this error
Use only one top-level statement in the project.
Top-level statements acts as an entry point to the program, so only one file may have top-level statement. All other statements must be defined as members of classes or structs.