Hi, 

Try like this,

return {
    'type': 'ir.actions.client',
    'tag': 'display_notification',
    'params': {
        'type': 'success',
        'message': "your success message",
        'next': {'type': 'ir.actions.act_window_close'},
    }
}

Thanks

Hi,

Try raise the success notification using below code.

Use your required messages.

message = _("Your required notification message.")
return {
    'type': 'ir.actions.client',
    'tag': 'display_notification',
    'params': {
        'message': message,
        'type': 'success',
        'sticky': False,
    }
}

Hope it helps