How do I enable Online Prebidding?
For silent auction pre-bidding the allow online pre-bidding option must be checked on an item (and should be by default for new silent items)
If you need to turn this on or off en-masse you can do this efficiently from the item list.
click the item list
click on the report menu and choose Open View
click on the Pre-bidding for silent auction choice
You will now see a column for Allow online pre-bidding and can edit each row either individual or use the mass change control.