Hi, How can I add an extra field in the DONORS for example parent's ID

Thanks for coming here today, president-lfm-om.

You can use the Custom form style feature and add a Custom field for your donors Parent's ID. I'd be happy to share the instructions below:

1. Go to the Gear icon and choose Custom form styles.
2. From the New style drop-down. choose a form (Invoice, Estimate, Sales receipt).
   
3. Choose the Content tab and click the first section of the form.
4. Scroll down and click the +Custom field. Enter Parent's ID.
5. Hit the Done button.
   

For more information about this process, you can visit this article: Customise invoices, estimates, and sales receipts in QuickBooks Online.

To test it, you can create a sample invoice for your donor and you will notice the added field for Parent's ID on the transaction. I've attached a screenshot for your visual guide:

If I can be of any assistance, please don't hesitate to leave me a comment below. Have a wonderful day ahead.