ActiveDEMAND provides data appending/enrichment services. These services are purchased using a 'credit' system.  The user buys Enrichment Credits and uses these credits to append data or create new records within an account.  Enrichment credits are managed from the billing section of your account (Administration  -> Account Billing)

Credits are purchased in blocks of 400 for $32 USD (8 cents/credit)

As long as there are Enrichment credits available, the data enrichment services can be used. You can set up AutoRecharge to ensure your credits are available when you need them. 

Data Appending Services

ActiveDEMAND provides two data appending services:

Data Enrichment Service

Learn About Data Enrichment

Reveal (identity resolution service) 

Learn About Reveal Identity Resolution