A technical portal could replace scattered attachments with a structured discussion about stage layout, inputs, sound equipment and access. Both sides need to know which version has actually been accepted.
The band could submit requirements while the venue marks items as available, unavailable or needing discussion. Attachments should have clear versions and dates. Changes after approval should reopen the relevant points rather than silently replacing the agreed specification.
Pilot the process with one venue and several different line-ups. Include missing equipment, a reduced stage size and a late personnel change. The portal can record an agreement and unresolved questions, but it should never imply that uploading a rider means the venue has accepted everything in it.
Related reading: ListnIN: How a Live Music Streaming App Connects Artists and Fans.