Kafka http sink connector regex.patterns/regex.replacements

I am enabling an http sink connector with multipe kafka topics. I would like to use kafka’s templating url feature with regex find and replace

the url form would be as follows example.com/{$topic}

the topic would be of form: this-is-the-topic-name

i would like to change it to this_is_the_topic_name

final url would be come : example.com/this_is_the_topic_name

the config is: Regular expression patterns: [-]*
Regular expression replacements: _