Second Ipad not connecting to Vodafone modem

Wonder if anyone would mind letting me have the benefit of much needed advice;

Just joined Vodafone home and although I can connect my own Ipad to the internet, my husband's will not connect. When he enters the security key, it is not being accepted, even though we were assured that all our devices could be connected.

Being not terribly au fait with technology, especially when switching providers, I would appreciate some advice please. Cannot work out what we are doing wrong and were not made aware of any process, other than entering the security key!