PERMISSION_DENIED: Search In Apps API has not been used in project

[patellaxya2]

I have put my API_KEY & CLIENT ID in the Android manifest
( just for ref my api_key is: AIzaSyA_TgvTBCYDspqkXXXXXXXXXX
CLIENT ID: test-search-in-xxxx
)
But after clicking on get suggestion button getting this error. can anyone please help me out with what went wrong here?
Please also mention the steps in which API/libraries need to be enabled.
PERMISSION_DENIED: Search In Apps API has not been used in project 755175XXX before or it is disabled. Enable it by visiting https://console.developers.google.com/apis/api/searchinapps.googleapis.com/overview?project=7551751XXX then retry. If you enabled this API recently, wait a few minutes for the action to propagate to our systems and retry.

Attaching app screenshot

I have also tried to search for "Search In apps" API SS Attached: