how to use "Stuff and 'For Xml Path'" to unite rows in table

Please help me to get united rows and list of accounts separated by commas in table. I don't quite understand how to use "Stuff and 'For Xml Path'" for it.

This is my query:

CREATE TABLE invoices
(
invoice VARCHAR(20) NOT NULL,
quantity INT NOT NULL,
price INT NOT NULL,
summ INT NOT NULL, 
account INT NOT NULL,
);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210110', 2, 100, 200, 1001);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210110', 3, 100, 300, 1002);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210110', 1, 250, 250, 1001);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210110', 2, 120, 240, 1002);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210110', 4, 100, 400, 1002);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210114', 3, 100, 300, 1001);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210114', 5, 80, 400, 1003);
INSERT invoices(invoice, quantity, price, summ, account) 
VALUES ('ty20210114', 5, 100, 500, 1004);


SELECT invoices.invoice, invoices.summ,  accounts = STUFF(
             (SELECT DISTINCT ',' + Convert(varchar, invoices.account, 60) 
              FROM invoices
              FOR XML PATH (''))
             , 1, 1, '')
FROM invoices
GROUP BY invoices.invoice, invoices.summ

This is what I get in result:

This is what I need to get in result:

So actually I need to get sums for 2 different invoices and to specify accounts by commas which involved to those invoices.

Also have this stuff at dbfiddle here: https://dbfiddle.uk/?rdbms=sqlserver_2019&fiddle=7a5de9e680693b5e70ea68cecebef6cc

Thank You in advance guys.

Don't group by summ if you want to sum it. Use sum() on it. And correlate the subquery. Otherwise you'll just get all accounts.

SELECT i1.invoice,
       sum(i1.summ) summ,
       stuff((SELECT DISTINCT
                     concat(',', i2.account)
                     FROM invoices i2
                     WHERE i2.invoice = i1.invoice
                     FOR XML PATH ('')),
             1,
             1,
             '') accounts
       FROM invoices i1
       GROUP BY i1.invoice;