calling an interface

Like any other expression rule.

https://docs.appian.com/suite/help/21.4/Expression_Rules.html#call-an-expression-rule-from-another-expression

docs.appian.com/.../using_interfaces_in_appian.html

hi, To call any child interface into a parent interface you can use prefix "rule!" and then interface name. For more details you can go through the link which stefanh0002 provided.