Error in conditional filter (if) syntax in sum function in SQL Server2005

The phenomenon and background of the problem

SQL server2005 in SUM Conditional filtering in function （IF） Grammatical errors

Problem related code , Do not paste screenshots

select SUM(IF(counts>0,counts,0) from testTable

Operation results and error reporting contents

Error message ：
news 156, Level 15, state 1, The first 1 That's ok
keyword 'IF' There are grammar errors nearby .
news 102, Level 15, state 1, The first 1 That's ok
',' There are grammar errors nearby .

My solution ideas and tried methods

Please help me to see where the grammar is wrong

What I want to achieve

Want to be in testTable Tabular counts Filter out all columns greater than 0 The sum of the values of