Invalid JSON
Check that you copied complete valid JSON. Send Listy can remove an outer fenced JSON code block before parsing, but the content inside the block still has to be valid JSON.
Missing items array
The imported list object must contain an items array. If the AI output uses a different structure, ask the AI tool to regenerate the list in the required JSON form.
Preview first
Use Preview to verify the parsed list name, type, item count, and content before selecting Use this list.