Do you offer an option to send automated follow up messages to my customers scheduled about other things except receipts and invoices ?

what kind of message? You may need a 3rd party app to do so.

Thanks for taking the time to reach out to us here, yuvalperry-inves.

We have a feature called Routines, and this is only available in QuickBooks Online Advanced. This allows you to send automatic reminders for your customer or yourself.

If you're subscribed to the Advanced version, you can enable the feature by following these steps:

1. Go to the Gear > QuickBooks Labs.
2. Scroll down to the Routines for QuickBooks section and select the toggle icon to turn the feature on.
3. Click Done.

Here's an article for more information: How to automate tasks with routines.

For QuickBooks Online Simple Start, Essentials, and Plus, you can upgrade to the Advance version or follow Fiat Lux - ASIA's recommendation to get a third-party application.

To search for an application, go to the Apps menu on the left panel.  

I'm just a post away if you have any additional questions or other concerns with QuickBooks Online. Thanks.