Spring Boot Placeholder Resolution Error: 'spring.datasource.pg.driver-class-name'

This error message typically indicates that Spring is unable to find the value for the specified placeholder in the application properties file. In this case, the placeholder is 'spring.datasource.pg.driver-class-name', which probably refers to the driver class name for a PostgreSQL database.

To resolve this issue, you should check the following:

1. Make sure that the application properties file exists and is located in the correct directory.
2. Check that the placeholder is correctly spelled and formatted in the properties file.
3. Verify that the value for the placeholder is defined in the properties file or in a configuration file that is included in the application context.
4. Verify that the PostgreSQL driver is included in the project dependencies and that it is correctly configured in the properties file.

If none of these solutions work, you may need to provide more information about your project and configuration to identify the root cause of the issue.