There are a several reasons why your device cannot find your account. For example:
1. Is the device logged into the same iTunes account as the one which the subscription was purchased under?
2. Have you recently changed devices?
3. Has any of your iTunes information, such as payment method changed? (expired credit cards would be considered a payment method change)
4. Does your device/iTunes need to be updated?
Here are some solutions that will likely resolve this issue.
1. Make sure that your device is logged into a correct iTunes account: Please see this article from iTunes: Sign in with Apple ID
2. Check to make sure that you do indeed have an active subscription. To do so, you will need to manage your iTunes account. For instructions click here: How do I manage my iTunes subscription?
3. Restart your device. Allow for a full reboot of your Apple device.
If these steps did not resolve your issue, please contact support
Recently switched over from Google Play? Click here:I recently switched platforms, how do I access my subscription?