Welcome to the Community forum, @craftvim-gmail-c.
In QuickBooks Online (QBO), the feature's available whether you're on Trial or Paid subscription are just the same.
Based on the information you provided, it appears that the gear icon you're referring is on the main page.
For you to be able to add a custom field on your invoice, follow these steps:
For visual guidance, see below screenshots:
To know more about this process, take a look at this article: Customise invoices, estimates, and sales receipts in QuickBooks Online.
Additionally, I want you to get the most out of QuickBooks for your business. You can check some articles that are designed to help you get acclimated to the software. They can be accessed at the following link: QuickBooks Tutorials.
Please let me know if there's anything else that I could help you with. I'll be here every step of the way. Have a great day!
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Thank you for your prompt reply. Be advised, if you're using QuickBooks Online Simple Start, the Custom Fields option isn't available.
Otherwise, let me share an alternative way for you to add custom fields to your QuickBooks Online (QBO) invoices.
Take your customization further by importing your custom form styles. See this article for additional details: Import custom form styles for invoices or estimates. This contains the step by step guide on uploading your custom form style, as well as a section with a list of common questions, along with their answers.
Feel free to place a question below if you have anything else in mind. I'll be sure to get back to you.
Thanks for reply @Ryan_M
I believe my 30-day trial version is "QuickBooks Online Simple Start" then because I cannot see Custom field name under Sales from content.
Please let me know which pricing plan includes custom fields?
You'll have to use QuickBooks Essentials, Plus, and Advanced so you can add custom fields in QuickBooks Online (QBO). Please check out this link if you'll want to avail of the 30-day free trial: https://quickbooks.intuit.com/global/gcsp/.
To know more about QuickBooks, please visit these helpful articles:
Feel free to let us know if there's anything else you need. I'll be here to help.
I also don't see this option. I used Quickbooks desktop since 2004 and printed professional looking invoices. With the new Quickbooks online, these invoices look like something my aunt would use from a Microsoft word template. I am a sole proprietor so have no need for all of the extras of upgrading and paying even more just to have a custom field. This online version brings me to tears a few times a week, and I'm getting ready to switch back to the desktop version. It's ironic that I pay more for this online version, but the simple things I used from desktop are not available unless I shell out even more money. Intuit really needs to get it together because I know I'm not the only one frustrated and disappointed with this non-user friendly version of Quickbooks online.