This is now defined in the problem statement near the end.

Not a kata issue.

select table schema
age [group by]
people_count (people count)

you want to group all the people by their age and count the people who have the same age.

It does say the expected name of the column and it's also in the error message.

In real scenarios you likely want a distinct in the count:

select age, count(distinct id) as people_count
from people
group by age

For some reason that doesn't work and does not return the right results in this kata.

Why do you need to order by species? It wouldn't accept my solution until I did but the problem description does not seem to indicate that it requires a specific order.