If you have an iOS device:

The subscription is connected to your Apple ID and the projects saved inside the app are connected to a particular device.

So it's not possible to work on one and the same project on multiple devices.

And to use one subscription, you need to share one Apple ID. You will need to log into your Apple ID in another person's device settings. Then open Instories on this device, tap on the settings menu in the upper left corner, then "Restore Purchase".

If you have an Android device:

Your subscription is connected to your Google Play account (if you downloaded the app from the Play Store) or your HUAWEI ID (of you got the app from AppGallery). Your projects saved inside the app are connected to a particular device.

So it's not possible to work on one and the same project on multiple devices.

And to use one subscription, you need to share one Google Play account or HUAWEI ID. You will need to log into your Google Play account or HUAWEI ID in another person's device settings. Then the subscription will be automatically restored in the app.

If you bought the subscription on the website https://instories.com/:

You can invite up to 20 members to your team and pay for their subscription.

You can add team members while creating your account on this step:

If you skipped this step or if you need to add more people later, follow these steps:

Go to the Members section in the menu on the left of the screen
Tap on Add members.
Enter email addresses and tap on Add.
To activate PRO license, a team member should open an invitation on their email on their mobile device and click the button or scan the QR code.

If you'd like to upgrade your personal subscription to a team account, please look for more info here: Can I create a team if I already have a personal account?