Have you signed up using the prentdo website first?
1707903657
Have you swapped networks on it first. Like on the prentendo app on the 3ds makw sure that's set to the pretendo servers first
Best bet is to Google uninstall reverse then attempt to reinstall pretendo.
That happened to me and was frustrating but the Uninstalling reverse worked a charm.
The stylus question is no the o3ds as a shorter stick compared to the 2ds and 3ds models and won't fit, it'll constantly fall out. And for the flap I need to see what you mean cos it could be the tiny cables either side need bending back.