Introduction
The IXG App for the IX | IXG Series system can perform the functions of AC Key. AC Key acts as an extension of AC Nio for the Aiphone Access Control system.
These instructions assume that the IXG App is already configured and functional on the phone, and that AC Nio has already been configured. See the appropriate Quick Start Guides if that is not the case.
IXG Support Tool: https://know.aiphone.com/quick-start-guides-ixg/
Remote Management for IX | IXG Series: https://know.aiphone.com/en_US/remote-management-quick-start-guide/remote-management-guide-table-of-contents
AC Nio: https://know.aiphone.com/access-control-instructions/ac-series-quick-start-guide
Procedures
Make sure that the app has been updated to the latest version to allow for the AC Key functionality.
Open AC Nio. Select the user whose app will be registered. If they do not already exist in the system, follow the steps in the AC Nio Quick Start Guide to add them.

Once the user exists in the system, navigate to Mobile Credentials. Set an email and click +Add Mobile Credential.

Fill in the name for the credential, set whether the user can create visitor passes, and the maximum allowed length for their passes. Click Save. An invitation will be sent to the selected email.

The user will receive the email. Click the enrollment link to enable the app.
Note: To use the IXG App instead of AC Key, make sure that only the IXG App is installed on the phone.

An end user license agreement will open in the phone's browser. Accept the terms.
The IXG App will now display an Intercom System mode and an Access Control mode. Tap the respective button to change modes.

See these instructions for the different app modes:
IXG App: https://know.aiphone.com/instructions-ixg-support-tool/ixg-app-operation-manual
AC Key: https://know.aiphone.com/access-control-instructions/ac-key-operation-manual (The Access Control mode under the IXG App will be identical to AC Key functionally, but the appearance may vary.)