Aaah, that explains it. That prompt didn't come up on my phone. Just a REF error. But when I used the link with a different login on my computer, I also got that prompt to accept urls and the images showed without any problems.
And you are not being nagging at all. Being informed about any errors I have missed is healthy for the project. And the wizard using a d8 was certainly an error. So thank you very much for catching that :D . I'll be making a small dev log to inform that the link have been fixed and the die error, and I would like to add your user name as credit. Will that be OK with you?
As for your sidequestion: I don't see why they can't mix it. The GM can after all add requirements if it becomes to wild. But for your specific example, I would say that they don't need to mix them, since most characters with spells/abilities that can manipulate a specific element, can usually also launch it in some form. Like rock, fire, ice, etc. So unless the player would find the other way more interesting, just let them launch some metal spikes.