MySQL doesn't have PIVOT syntax. Has to be assembled using basic sql ops.
Two stages in the logic ...
1 build the list of possible pivoting values,
2 work that list into a query that outputs their sums
Your didn't provide your DDL or sample data, so I built a toy table from your SQL Server code ...
drop table if exists remission;
create table remission (client varchar(64), datepay date, total decimal(8,2) );
insert into remission values
('a','2020-1-1',1000),('a','2020-1-15',1000),
('b','2020-1-1',1100),('b','2020-1-15',1100),
('c','2020-1-1',1200),('c','2020-1-15',1200),
('d','2020-1-1',1300),('d','2020-1-15',1300);
Here's the simplest way I know to pivot datepay on client summing amount in MySQL ...
-- 1 assemble pivot expressions
SELECT
GROUP_CONCAT(DISTINCT
CONCAT(
'sum(if(datepay = ''', datepay,
''', total, 0)) AS `', datepay ,'`'
)
)
FROM remission INTO @sql;
-- 2 assemble query around the above result
SET @sql2 =
CONCAT( 'SELECT t.client, ', @sql, ' FROM (
select client, datepay, total
from remission
)t
group by t.client
order by t.client');
PREPARE stmt FROM @sql2;
EXECUTE stmt;
DROP PREPARE stmt;
+--------+------------+------------+
| client | 2020-01-01 | 2020-01-15 |
+--------+------------+------------+
| a | 1000.00 | 2000.00 |
| b | 1100.00 | 2100.00 |
| c | 1200.00 | 2200.00 |
| d | 1300.00 | 2300.00 |
+--------+------------+------------+