I'm trying to parse a webhook response to remove some brackets by utilizing the "substringBetween()" function like this:
{{webhookResponse.body.schedules.schedule.onCallUser.username.substringBetween("[","]")}}
Without the substringBetween function, the value returned is "[user]"
When I check the audit log when using the function, it appears that it's _only_ capturing the brackets as shown here:

Am I using this function incorrectly?