Hi Rebecca
The & character is a predefined entity reference in the XML syntax. Refer to the link below:-
Therefore you cannot use it as-is within the content of an XML element tag. This will cause the whole XML to be invalid. To correctly represent the character & within an XML element tag, you need to replace it with & instead.
As Amit has mentioned, you are manually entering the XML data (which is invalid) when using the test proxy functionality.
Change the line to the below instead:-
<URL>Username&Rebecca&Password</URL>
Rgds
Eng Swee