Document Sequence category Expense Report vs Payment Request (Document Sequence Category Name)

Summary:

I am configuring the "Document Sequence" for the Expenses module. Under the Assigment section, I see two categories : "Expense Report Invoices" and "Payment Request". When is Oracle using one or the other ?(Document Sequence Category Name)

Content (please ensure you mask any confidential information):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):