Conversion Sql From Oracle To SQL Server

Hi Guys, I have this statement that I am converting from Oracle to SQL. Help pls:-) PP_PRICEPOINT_ID is a decimal. What is the appropriate usage..

Oracle
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update pricepoint set pp_type = decode(substr(pp_pricepoint_id,1,1),7,0,2),
pp_qtybreakindex =substr(pp_pricepoint_id,3,1) where pp_type is null and pp_qtybreakIndex is null;

Here is its SQL
-----------------
UPDATE pricepoint
SETpp_type =
CASE SUBSTRING(pp_pricepoint_id, 1, 1)
WHEN 7 THEN 0
ELSE 2
END,
pp_qtybreakindex = SUBSTRING(pp_pricepoint_id, 3, 1)
WHERE pp_type is null
ANDpp_qtybreakIndex is null
----------------
I am getting the error
The data type decimal is invalid for the substring function. Allowed types are: char/varchar, nchar/nvarchar, and binary/varbinary.