With some devices it can happen that the charging cable has to be released first.
To do this, unlock your end device after connecting the allroundo® to confirm a possible pop-up.
It also helps to activate the switch and secure a data transfer under Settings → Code → USB accessories.
Also check if your iPhone and radio have the latest software version.
Please note that CarPlay is not supported by allroundo® Classic from third parties or the Telekom Mega Deal.