When working with URLs, pay particular attention to the use of the question mark (?), which is a special character that requires escaping with the backslash, for example: "/page\.html\?param1=value1" (the dot "." is also a special character).
When using regexes in variable extractors, do not forget to use parentheses to define the various groups. The " .*" and "(.*)" patterns may both match an expression, but only the pattern enclosed in parentheses will extract the value by referring to the group using $groupNumber$. In certain cases, parentheses need to be used to isolate part of a regex pattern, regardless of any group definition requirements. This must be taken into account when defining the groups whose values are to be extracted.
A space is a normal character that must be taken into account in regexes. Check to make sure there are no extra spaces at the start or end of the regex, especially after cutting and pasting.
The characters ".*" mean "matching any string of characters except line breaks". If the expression is tested over several lines, use "([^^]*?)", which includes line breaks.