Your Maltego Graph application comes with access to standard Transform sets in the Data Hub and access to free and paid Connectors in the Data Hub determined by your Maltego Plan.
Data Hub items in the Connectors listings in the Data Hub are provided through third-party Transform partners and require an additional API key from the provider in order to use their Transforms.
To get an API key from a third-party Transform provider you will need to contact the provider directly. You will be able to find their contact details on the Data Hub as shown below: