Sub audit has to be created before parent audit creation.
To create a sub audit select the option Configure audit, click on Create audit type, create Audit type name (name Sub-audit).
Select the Auditee type (auditee type like Branch, Vendor, Agency, Warehouse, etc), go to Next, define Audit type by group, select Group type (General/Annexure), then select checkpoint group and Submit. While creating the sub-audit, do not click on the parent audit.
Here you go Sub audit is created.
