MediatR - System.Text.Json.JsonException: 'S' is an invalid start of a value.

var command = new CreateUserCommand(userReq.Email);
var createUserResult = await mediator.Send(command);

My command:
public record CreateUserCommand(string Email) : IRequest<ErrorOr<User>>;

My handler:
  public async Task<ErrorOr<User>> Handle(CreateUserCommand command, CancellationToken cancellationToken)
    {
        var user = await _userRepository.CreateUser(new User(){Email = command.Email});
        await _unitOfWork.CommitChangesAsync();
        return user;
    }

I Register my MediatR like this:
 services.AddMediatR(options =>
        {
            // options.RegisterServicesFromAssemblyContaining(typeof(DependencyInjection));
            options.RegisterServicesFromAssembly(typeof(DependencyInjection).Assembly);
        });

mediator.Send(command);