I am trying to add Service Address to my invoices. I am under Account and Settings > Sales > Sales form Content ... but there is no option to add Custom fields. Help?

I'll be happy to help add the custom fields, @arianne-kcngroup!

You're on the right track, custom fields from the old versions of QuickBooks are found under your sales form content. Now, the ability to add custom fields is integrated on your lists from the gear settings. I'll show you how.

1. Go to the Gear icon.
2. Under LISTS, select Custom fields.
3. Select Add field.
4. Enter Service Address as the name of your new custom field.
5. Put a checkmark on the All Sales forms selection.
6. Toggle to turn on the Print on form option.
7. Click Save.

I'm adding this article discussing how you can add a custom field: How to Add Custom Fields to Sales Forms and Purchase Orders in QuickBooks Online?

Once your invoices have been created, use this reference for ideas about the other methods you can start using in accepting payments from your customers: Record Invoice Payments in QuickBooks Online.

Keep me updated in the comments if you have any other questions other than adding custom fields. I'll be here to lend a helping hand. Take care and stay safe!

Custom fields is not an option under lists.

My options are:

All lists (more on this below)

Products and services 

Recurring transactions 

Attachments

Tags

Under all lists, the closest option I have is Custom Form Styles but that only lets me choose from teplates already there and does not allow me to add a custom field.

That is not an option under Lists.

My options are

All lists

Products and services 

Recurring transactions 

attachments

tags

All lists is a sub section but it only has Custom Form Styles. That has templates but no option for individual custom fields

I appreciate you for getting back, Arianne. I'm here to share with you some additional information about the custom fields feature in QuickBooks Online (QBO).

Adding custom fields to your sales forms as instructed by JonpriL above is available in QBO Essentials and Plus. The feature gives you more flexibility to add custom data to your transactions and drive insights through your reports. If you aren't subscribed with either the Plus or Essentials plan, you can consider upgrading your upgrading your account to add service addresses to your invoices.

Otherwise, you can personalize your invoice template to add the field from there.

1. Go to the Gear icon, then click on Custom Form Styles.
2. Select the template you're using, then click on Edit under Action.
3. Go to the Content section, then tap on the upper part of the PDF page. 
4. Make the necessary customization, then add a custom field from there.

To learn more about setting up custom fields in QBO, you can check out this article: How to add custom fields to sales forms and purchase orders.

And, here's how you can use enhanced custom fields in QBO Advanced: Create and edit custom fields in QuickBooks Online Advanced.

If you have any other questions about customizing your sales forms in QBO, let me know by adding a comment below. I'm more than happy to help. Wishing you a good one!

No, I apparently don 't have the Essentials plus.  I will not be upgrading at this time.

The other solution does not work.  It won't allow me to make any changes beyond clicking on pre-provided fields.  I can't even get "Estimates" to show because I tried changing that field name to Service Address.

I followed the instructions in the link you provided but I apparently do not have a version that will allow for this.  I'm just going to have to put it in the Notes section.