Add Field Option is greyed out in QB Online

The reason why the Add Field option is unavailable when attempting to add a PO to your invoice in QuickBooks Online (QBO) is because of certain limitations, David. 
 

For QBO Simple Start, Plus and Essential subscriptions, you can create a minimum of 3 custom fields. Additional information can be found in this link: Set up custom fields. If you want to add more than 3 fields, you'll need to upgrade to Advanced.

If you wish to create personalized and professional looking invoices, estimates, and sales receipts, check out this link. 

If you have any further question about adding custom fields or need assistance with upgrading your plan, please don't hesitate to ask. We are here to help you successfully include a purchase order on your invoice. Have a good one. 

Well the problem is I migrated a 1-2 month file last night to QBO, so we are day 1/2 or 1.  I have not made any custom fields yet, so def not hitting the 3. 

I did see on the new price lists were custom fields are only in Advanced.  That seems really crappy to me.  Having a PO on teh invoice is one of the most basic accounting functions, or should we call Simple.   I didn't have any custom fields on my 1-2 month old 2019 QB Desktop for MAc.  Just the basics while I was getting going.

I appreciate the answer and feedback.  Thank you!

I have a similar problem. It's greyed out, BUT I do not have any active custom Fields

Thanks for joining the thread, DDIFede. 

Considering you already know about the custom field limits for Simple Start, Plus, and Essentials subscriptions and have confirmed that no custom fields are currently active, let's move forward with some troubleshooting steps to fix this.

Internet browsers can store temporary cache that sometimes cause conflicts with web applications. Clearing these can often resolve unusual behavior. Here’s how to do it on some common browsers:

1. Use an Incognito Window: Log in to your QuickBooks account in an incognito window to avoid browser-specific issues.
   - Google Chrome: Press Ctrl + Shift + N
   - Mozilla Firefox and Microsoft Edge: Press Ctrl + Shift + P
   - Safari: Press Command + Shift + N
2. Clear Cache and Cookies: If accessing QuickBooks through the incognito window works, clear your browser’s cache and cookies. This resolves loading and formatting issues caused by store cache. 
3. Switch Browsers: If the issue persists, use a different supported browser, as your current one may have a temporary compatibility issue with QuickBooks.

These steps should help address the greyed-out Add Field issue. To delve deeper into customizing your sales forms, you may find this resource useful: Customize invoices, estimates, and sales receipts in QuickBooks Online. It provides detailed instructions on how to incorporate various elements to make your forms reflect your unique business style.

On another note, I’d like to highlight the support available from our QuickBooks Live Expert Assisted team. Their expertise can significantly enhance your financial management, ensuring that your processes are efficient and well-managed.

Should you need further assistance or have more questions down the road, feel free to reach out through the thread. I’m ready to dive back in whenever you need. Take care.