Permission issue when writing/updating with apoc.periodic.iterate

I am connecting through bolt protocol to a Neo4j Server instance.
When using apoc.periodic.iterate to set a property (calling apoc.ttl.expire), I get errors like this:

"org.neo4j.graphdb.QueryExecutionException: Set property for property 'ttl' on database 'neo4j' is not allowed for user 'andrea' with roles [PUBLIC, admin] overridden by TOKEN_WRITE overridden by READ."

Why is that if I should be assigned an admin role? Why do those final "overridden by.." occur?