Materiality is the primary consideration when determining which issues to include in an audit report, as it reflects the significance or importance of the issues to the users of the report. Materiality is a relative concept that depends on the nature, context, and amount of the issues, as well as the expectations and needs of the users. Materiality helps the auditor to prioritize the issues and communicate them clearly and concisely.
References
ISACA CISA Review Manual, 27th Edition, page 256
Materiality in Auditing - AICPA
Materiality in Planning and Performing an Audit - IAASB

The most appropriate testing approach when auditing a daily data flow between two systems via an automated interface is to perform data reconciliation between the two systems for a sample of 25 days. Data reconciliation is a process of verifying that the data transferred from one system to another is complete and accurate, and that there are no discrepancies or errors in the data flow1. Data reconciliation can be performed by using generalized audit software, which is a type of computer-assisted audit technique (CAAT) that allows the IS auditor to perform various audit tasks on the data stored in different file formats and databases2. By performing data reconciliation for a sample of 25 days, the IS auditor can test the reliability and consistency of the data flow over a reasonable period of time, and identify any potential issues or anomalies that could affect the quality of the data or the functionality of the systems.
References
1: Data Flow Testing - GeeksforGeeks 2: Generalized Audit Software (GAS) - ISACA

Issuing authentication tokens is the most reliable method of preventing unauthorized logon, as it provides a strong form of authentication that requires users to present something they have (the token) and something they know (the personal identification number or PIN) to access the system. Authentication tokens are physical devices that generate a one-time password or code that changes periodically and is synchronized with the authentication server. This makes it difficult for attackers to steal or guess the credentials of legitimate users. Reinforcing current security policies, limiting after-hours usage and installing an automatic password generator are not as reliable as issuing authentication tokens, as they do not provide a strong form of authentication and may still be vulnerable to unauthorized logon attempts. References:
* : [Authentication Token Definition]
* : Authentication | ISACA