1) Three key challenges in big data for PersuasionAPI are focusing on meaningful data, moving from analytics to advice, and handling the inability to analyze all data. 2) To address these, PersuasionAPI identifies persuasive strategies, selects distinct strategies for individuals, and adapts recommendations based on individual responses. 3) PersuasionAPI provides real-time advice on strategy use for each customer by summarizing data for direct recommendations between page views and improving profiles over time. It uses online learning and hierarchical models to deal with large amounts of data.