Thanks for your detailled reply.
So I need a dedicated Hubspot Developers Account to use the Templates API?
Because we have just regular Hubspot accounts (prod & test) with the above mentioned APIs working.
Can we link those after creation? Or how do we connect the created private apps?
Also what are the Custom Events good for in the regular Hubspot GUI (with “Send via API” option), if not for this particular usecase?