Athletics.app will only display a sequence number for reserves if you let Athletics.app manage them automatically.
You can set whether and how you want Athletics.app to manage reserves for each category / event.
This can be done through the Wizard, Step 7b 'Entry Limits / Maximum Number of Competitors'.
Only if you select 'Entry Time (Automatic)' or 'Best Performance (Automatic)' there will sequence numbers for reserve athletes appear.

More information on the various automatic options for managing reserves can be found here: https://www.athletics.app/faq/?qa=104/reservelijsten-bijhouden-voor-pinkstermeerkamp
This has been automatically translated into English