Graphql/Prisma2/ Error creating a database connection. (Operation timed out (mobc timeout))

I am actually developing with prisma 2. and it worked on my local development. (every query.)

However , when I deploy them on heroku, it doesn’t work on playground. I don’t know what happend.

I made db at the AWS (free tier + postgres)

Do you have Any idea with this error msg below?

{
      "data": null,
      "errors": [
        {
          "message": "Error creating a database connection. (Operation timed out (mobc timeout))",
          "locations": [
            {
              "line": 2,
              "column": 3
            }
          ],
          "path": [
            "codeByCode"
          ]
        }
      ]
    }