Try this
var text $URLONE=
URLRoot() & "db/" & Dbid() & "?act=API_EditRecord&apptoken="appToken"&rid=" & [Record ID#] & "&_fid_41="&URLEncode("Sales Feedback");
var text URLTWO = URLRoot() & "db/" & [_DBID_of the child table found in advanced properties]
& "?act=API_AddRecord"
& "&_fid_xx=" & [Record ID#] // populate the field [related parent] with the record ID# of the parent you are sitting on
& "&_fid_10=" & urlencode([field 1])
& "&_fid_20=" & urlencode([field 2])
& "&_fid_30=" & urlencode([field 3]);
& "&apptoken="appToken";
var text URLTHREE = urlroot() & "db/" & dbid() & "?a=dr&rid=" & [Record ID#];
$URLONE
& "&rdr=" & URLEncode($URLTWO)
& URLEncode("&rdr=" & URLEncode($URLTHREE))
Note that the normal way to "populate" a child record with data from the parent is to simply add a lookup field to the relationship, but maybe you have some unique requirements here.