Can not backup multiple (not all) databases Ola Hallengren
If you examine the code for DatabaseBackup.sql, you'll see that the definition for the parameter @Databases is @Databases nvarchar(max) = NULL.  When passing in literals like DB1, DB2, etc., the entire string needs to be surrounded by single quotes - (just like you used for literals for other parameters).

EXECUTE [dbo].[DatabaseBackup]
@Databases = 'DB1, DB2, DB3',
@Directory = N'C:\Temp',
@BackupType = 'FULL',
@Verify = 'N',
--@CleanupTime = 360,
@CheckSum = 'Y',
@LogToTable = 'Y',
@NumberOfFiles = 4