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No Change or Join Button

Only parents are able to see a change/join button to add items to hiking and activity logs.

How can Unit Advancement Chair or Cubmaster add that info for the Packs?

The CM should be able to see it in IA already. Have the CC check in the fleur de lis pull-down in the upper right corner to make sure that their CM position is selected.

For the UAC, they have to be designated in the Organizational Security Manager in my.scouting.org by one of the unit Key 3 (CM/CC/COR) as either a Key 3 Delegate (more access than they likely need) or as the Unit Advancement Chair. This is separate from designation in Scoutbook.

ETA:

More infor here: How Do I Record a Unit Activity Using Internet Advancement (IA) | Scoutbook Knowledge Base