Add extra fields in Donors masters like id. We require primary ID field as well.

Good day, president-lfm-om.

I can help and share some insights regarding adding an extra field for Donors ID in QuickBooks Online.

You can use the Other field to enter the Donors ID information since adding extra field is currently unavailable in QuickBooks Online.

Or, you can add the ID information under the Notes tab. Once added, this will show on your donor's profile.

I'm sharing with you the following write-ups below. This will provide you more information about merging donors as well as steps on how to designate inactive donors in QuickBooks Online:

Manage your customer list

Edit customer information

If there's anything else you need please let me know. I'll be around to help you out.