If You using forms (Start Custom form from the SharePoint List), prepare the validation:

1. On screen Visible
   set the default variable to show error
   [code]UpdateContext({

   showValTask: false,
   showValSomeOther: false,
   ….
   });[/code]

2. Set the Text property for the error message
   
3. set error label
   Visible = showValTask
   

4. Hide the validation on the InputBox when do any changes
   OnChange UpdateContext({ showValTask: false})

    

5. Finally do the validation OnSave [code] If(showValTask || showValDescription || …… ,
   UpdateContext({locIsAllValid: false}),
   UpdateContext({locIsAllValid: true})
   );

   If(
   !locIsAllValid,
   Notify(
   "An Form entry is required or has an invalid value. Please correct and try again.",
   NotificationType.Error,
   4000
   )
   );

   If(
   locIsAllValid,
   SubmitForm(frmNew);
   UpdateContext({locRecord: frmNew.LastSubmit});
   Refresh(Submissions)
   );
   If(
   locRecord.ID > 0,
   Notify(
   "Deliverable has been Updated!",
   Success,
   5000
   );
   Navigate(scrGalleries, ScreenTransition.Cover);

   ) [/code]