Explanation
The best way to address the concern that data collected by a third-party vendor and provided back to the organization may not be protected according to the organization's privacy notice is to validate contract compliance. This means that the organization should verify that the third-party vendor is adhering to the terms and conditions of the contract, which should include clauses on data protection, privacy, and security. The contract should also specify the obligations and responsibilities of both parties regarding data collection, processing, storage, transfer, retention, and disposal. By validating contract compliance, the organization can ensure that the third-party vendor is following the same privacy standards and practices as the organization.
References:
* ISACA, CDPSE Review Manual 2021, Chapter 2: Privacy Governance, Section 2.3: Third-Party Management, p. 51-52.
* ISACA, Data Privacy Audit/Assurance Program, Control Objective 8: Third-Party Management, p. 14-151

Explanation
Data flows are the most important to review before using an application programming interface (API) to help mitigate related privacy risk. Data flows are the paths or routes that data take from their sources to their destinations through various processes, transformations, or exchanges. Data flows can help understand how data are collected, used, shared, stored, or deleted by an API and its related applications. Data flows can also help identify the potential privacy risks or impacts that may arise from data processing activities involving an API and its related applications. Data flows can be represented by diagrams, maps, models, or documents that show the sources, destinations, types, formats, volumes, frequencies, purposes, or legal bases of data.
Data taxonomy, data classification, and data collection are also important for privacy risk mitigation when using an API, but they are not the most important. Data taxonomy is a system of organizing and categorizing data into groups, classes, or hierarchies based on their characteristics, attributes, or relationships. Data taxonomy can help understand the structure, meaning, context, or value of data. Data classification is a process of assigning labels or tags to data based on their sensitivity, confidentiality, criticality, or risk level. Data classification can help determine the appropriate level of protection or handling for data. Data collection is a process of gathering or obtaining data from various sources for a specific purpose or objective. Data collection can help obtain the necessary information or evidence for decision making or problem solving.
References: Critical API security risks: 10 best practices | TechBeacon, Open APIs and Security Risks | Govenda Board Portal Software, The top API security risks and how to mitigate them - Appinventiv