Welcome 
…
…well… if you may explain this a bit more than only using a semi-sentence as title and also a bit more precise than “I did everthing correct but it doesn’t work…” because:
- which blender version
- you are using cycles ?
- you have enabled the Visibility → Mask: Shadow Catcher (you write of shadow only) ?
- the back ground uses is also very greyish and so the shadow may be bot seen very well: maybe also because of very light light ( ← pun intended)
- and finaly: obviously something is wrong… but showing the result only is not much of any hint…
So you may help the community to better be able to help you ?
( Maybe also spending some minutes in the forum to be able to post the blend file… ?? background image not needed; please use the compress option of blender…)
some clicks later
