When the deck title of a deck is more than 118 characters long, you can't copy the deck, because copying a deck adds "Copy of - " to the deck title, which is 10 characters, and the max length is 128.

{"ops":[{"insert":"Title explains the thread.\n\nIt then gives you an error message titled: \n\n"},{"attributes":{"bold":true},"insert":"Deck creation failed"},{"insert":"\nUnexpected token < in JSON at position 0\n\nI'd just do a character length check, and remove last bits of the title to add the \"Copy of -\" part.\n\nExample: "},{"attributes":{"link":"https://archidekt.com/decks/809352#[EDH]_Obuun_the_Valakut_Ancestor,_But_You_Can't_Copy_The_Deck_If_The_Name_Is_Longer_Than_118_Characters,_Who_Even_Does_That"},"insert":"https://archidekt.com/decks/809352#[EDH]_Obuun_the_Valakut_Ancestor,_But_You_Can't_Copy_The_Deck_If_The_Name_Is_Longer_Than_118_Characters,_Who_Even_Does_That"},{"insert":"\n"}]}