Share Cloud SQL DB between 2 projects with app engine

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Hi, 

I have a postgres Cloud SQL DB instance in my project A, it works perfectly with my django project on App Engine of project A. 

Now I have developed a project B and I would like to share the DB instance with project B. 

I put the same host as project A in the settings file of project B like:

/cloudsql/project-285409:europe-west4:project-A-DB

but when I deploy project B on app engine, django keeps having connection error 

could not connect to server: Connection refused   

Is the server running locally and accepting connections on Unix domain socket "/cloudsql/project-285409:europe-west4:project-A-DB.s.PGSQL.5432"?

I have enabled Cloud SQL API

Did I miss some settings or it is not possible to share DB between 2 projects?

Thank you

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Ok

 solution found. 

Just need to add service account of ProjectB to IAM of ProjectA