"The concept was good."
Übersetzung:Das Konzept war gut.
z.B. von hier:
"Das ist ein dehnbarer Begriff"
"Der Begriff von Freiheit"
I'm not a native, but I would think of Begriff as a theoretical formulation or a general idea, while I would think of Konzept as a draft or a sketch, an initial idea of what one wishes to fully develop and implement at a later time. Without context, Begriff should definitely be accepted.