How to select best customers and group them by how much they paid

I am using SQL server to select this table and group the customer id and first name according to their total payments made to the store. I tried using

select custid, name, sum(payment)
from transactions
group by custid
order by payment desc

but it returns the following error:

not contained in either an aggregate function or the GROUP BY clause

Could you please clarify what I did wrong?

this is my customer table

cust id	payment	name
T001	60	katy
T002	12	amy
T003	40	leon
T001	20	katy

this is the result table I want to get

cust id	payment	name
T001	80	katy
T003	12	amy
T002	40	leon

Answer

The error refers to the name or payment columns, both of which you refer to without aggregating.

You need to order by the same expression or provide the column an alias; column name inconsistencies aside, try:

select Cust_Id, sum(Payment) as TotalPayment, Name
from transactions
group by Cust_Id, Name
order by TotalPayment desc;