The 1 in the handlebars should refer to a variable that should be used afterwards. for example - {{regexExtract request.body 'token%3D([a-f0-9\-]+)' 1 default='unknown-token'}}

should be {{regexExtract request.body 'token%3D([a-f0-9\-]+)' 'parts' default='unknown-token'}}{{parts.1}}

Now it works