This error occurs when looping over an array with Angular using the *ngFor syntax.
core.js:9847 NG0303: Can't bind to 'ngForIn' since it isn't a known property of 'x'.
This was my code:
<ion-item lines="none" *ngFor="let notification in usernotifications">
Use the correct syntax, use "of" instead of "in"
<ion-item lines="none" *ngFor="let notification of usernotifications">