Unable to get record while using the double backslash in swagger using get function with parameters

I've two parameters like Register No. and UserName. I Entered Register No. Like "###$$$$%%%%" and UserName Like "TESTPC\TEMP" than result is successful but no record shown.
Instead of above if I Entered. Like
UserName. I Entered Register No. Like "###$$$$%%%%" and UserName Like "TESTPC\TEMP" than record is displayed.

Question: What is the difference between that. Because I posted record with double slash but in SQL server its shown single. so how do i specify a value for UserName at run time.

Thanks.
Jeegen