Unfortunately you will need to put the sim card into a cellphone.
You will need to do this as Afrihost needs consent in order to manage your account.
Once you've done with that, the sim card will work 100% and you can then put it back into your Mifi device.
However, this means you won't be able to use your airtime minutes, as the mifi device only caters for mobile data.
I hope that helps, enjoy your evening!