I might have found a workaround: When you open the detail page of the transaction for your initial investment, it is displayed just like any other transaction to one of your own sub-accounts. Now if you tap on the symbol of the Investment Goal as your “recipient”, you get to a detail page where an IBAN is displayed.
I was able to make a normal bank transfer to that IBAN and it now appears in my Investment Goal account, waiting to be invested. I cannot try it for myself but perhaps you can try setting up a recurring payment in that way?
Sorry for the bad explanation. I hope it’s understandable!