For a Bill Payment, I try to create a Transaction Saved Search and list all Bills and Bill Credits for a Bill Payment. I can list the Bills, but not the Bill Credits. I have tried using the APPLIED TO TRANSACTION FIELD.., but I am only getting blank values. How do I list Bill Credits for a Bill Payment?

Are you sure you have Bill Credits applied to a Bill Payment? Have a look at this table: https://netsuite.custhelp.com/app/answers/detail/a_id/92641/kw/transaction%20applied%20to%20search

From what I remember here and my personal experience, Bill Payments and Bill Credits are not linked (at least in saved search). You might want to use Type = Bill instead so you can capture both or try SuiteAnalytics Workbooks.