AssemblyDoesNotExist when sending strings

[JustAnotherGameDevWasTaken]

both client and server have the System library in the project. code below:

called on client after connection:
connection.RegisterStaticPacketHandler<Common_Packets.Test2>(Testing2);
connection.Send(new Common_Packets.Test("Hello"));

called on server after connection:
Console.WriteLine($"{connectionType} Connection received {connection.IPRemoteEndPoint}.");
connection.RegisterStaticPacketHandler<Common_Packets.Test>(Testing);

both have these as packets:

[Toemsel]

Can you provide a minimal example project?

[Toemsel]

No response received.