The error message suggests that the macro "PUBLIC_TWITCH_CAP_ALL" has not been defined, which doesn't make much sense - did the scripts import correctly? The macro is defined in "twitch_connect", so you might have to check that script to see if it has loaded correctly.
I'm a little confused by the second question - I don't believe I used any sprites in the demo project, nor in the video - could you clarify what you mean please? Pictures may help me understand.
Yes, you can modify the demo to send messages to Twitch quite easily!
I think the simplest way is to do something like this:
Add a key press event (I chose Key Press Enter) and add this code to it:
if(twitch_check_connected())
{
twitch_send_chat_message(get_string("Send Message","message"));
}
If the demo is currently properly connected to a twitch chat, this will open a textbox when enter is pressed, and will send the message once confirmed.
For non-test purposes, you should use async input functions - or better yet, custom text inputs - but this test code gets the job done in a simple enough way.
I don't know if it is possible to send DMs on itch, but you can send an email to MaddeStudios@gmail.com if you want!