I created a custom block, I can't seem to add it to a topic page. I was able to successfully add it to a forum list and the home page though.

Sometimes I get this error:

And sometimes I get this:

Please could you let me know the name of the block?

class-banner

....aaand just now I was able to make it work. It showed an error as in my first screenshot but then when I reloaded the page it worked.

Happy to help