I'm studying about the mediator pattern. I would like to register a handler to handle a command that has a generic type, where the type is an IMessage.

internal class NewEmployeeCommand<TMessage> : IRequest
    where TMessage : IMessage
{
    public string Name { get; init; }
}


internal class NewEmployeeCommandHandler<TMessage>
    : IRequestHandler<NewEmployeeCommand<TMessage>>
    where TMessage : IMessage
{
    public async Task<Unit> Handle(
        NewEmployeeCommand<TMessage> request, CancellationToken cancellationToken)
    {
        /* DO SOMETHING */

        return Unit.Value;
    }
}

When trying to send my command using await mediator.Send(command), I'm getting the following exception:

Error constructing handler for request of type MediatR.IRequestHandler. Register your handlers with the container.

I've already tried to configure dependency injection in several ways, but all without success:

services.AddTransient<IRequestHandler<NewEmployeeCommand<IDevMessage>>,
    NewEmployeeCommandHandler<IDevMessage>>()
services.AddTransient(
    typeof(IRequestHandler<NewEmployeeCommand<IDevMessage>>),
    typeof(NewEmployeeCommandHandler<IDevMessage>))`

Can anyone help me where I'm going wrong? I'm using ASP.NET Core 6.