Cannot connect

Hello! I am trying to understand Neo4J Version 4.2.1 and how it is used in R. I am using the localhost:7474 as my url with the Neo4R package in R. However whenever I navigate to that website to find out my username and password, the link is broken. I tried logging into Sandbox with some other projects to see the connection details and tried adding those credentials but it did not work.

con <- neo4j_api$new(
url = "http://localhost:7474",
user = "neo4j",
password = "password"
)

When I try to use the default password and username, I get the following error after using the command con$ping...

con$ping
Error: Failed to connect to localhost port 7474: Connection refused

I might be missing something here, but you mentioned only sandbox, so localhost:7474 is not going to work.
Are you running a Neo4j server locally on your machine?

From my understanding, I need a version of Neo4J that is 3.5.x. However, I am having problems finding a version on the website

You can use a 3.5 Docker image if you want to try it out: Docker Hub

I found out how to change the version to 3.5.x. However, I am experiencing problems with the password.

You might want to try this R project / CRAN package to connect to Neo4j from R. It uses the Neo4j cypher-shell command line tool to send queries and retrieve data from the graph which makes it fairly lightweight implementation.