Thanks for your answer. But why does the doc say the following?
"With Block.io, you can create wallet addresses for users inside your games, auction sites, stores, etc.
To create a user's wallet on your account, create addresses for them using get_new_address. You should specify a sequence of labels for that user. For instance, if you wish to create a number of addresses for User A, you would want to call get_new_address with label=userAx{address_number} as many times as you wish to create a new address for User A.
Once you have addresses for User A, you can perform relevant actions for their addresses."
And that's exactly what I want to do in PHP. I remember that it could be realized via block.io with forwarding_addresses some time ago. But that is apparently no longer possible, for whatever reason.
And yes, you are welcome to ask. I'm building some kind of asset safe for friends with some features. The user should simply be able to generate a new receiving address, which can also be clearly assigned to his wallet.