Mixed Authentication Support for Nintex App Studio
Does Nintex App Studio support Mixed Authentication for SharePoint with Forms Based Authentication (FBA)?
Nintex App Studio does not support Mixed Authentication for SharePoint out of the box. When a SharePoint environment has both Windows Authentication and Form Based Authentication configured, Nintex Mobile will only support Windows Authentication by default.
However, you can use the following steps to put in place an IIS redirect which will allow Nintex App Studio to authenticate through FBA even when Windows Authentication is enabled:
Enable FBA Access within Central Administration > Nintex Forms Management > Manage FBA Mobile Access.