am getting this error message
{ "code": "Neo.TransientError.Database.DatabaseUnavailable", "message": "Requested database is not available. Requested database name: 'graph.db'." }
while sending a request through rest API, with this statement
{ "statements" : [ { "statement" : "CREATE (n) RETURN id(n)" } ] }
I'm guessing you probably don't have a database called graph.db. That is the name of the file system directory, not the database. Unless you've set up a database yourself, use neo4j, which is the default.
As Nigel said, it'll be because you don't have a graph by that name. I ran into this issue recently, after upgrading from 3.5.3 to 4.1, and having to figure out some new behaviours (why yes, I have been living under a rock).
Read through the server's logs - it reports the database name while it's starting up. If you're using a Docker instance, as I am, docker logs <instance-id> is your friend.
