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If many devices cannot connect to the iPad, then try this:
on the iPad, go into Settings
go into Wireless settings (or Network settings, then Wireless settings)
and disable (or, set to Off) the 3G or 4G networking
(and check that WiFi is enabled.)
That may free it up to be connected to... having 3G/4G networking enabled may block WiFi networking functions.
(If you are trying to use Bluetooth
networking with the iPad instead, then disable 3G/4G, and also turn Off WiFi, just leave Bluetooth enabled. Same story.)