Hi Sandy312!

I'm taking over since Kurt's shift has ended. You need to be on the Essentials or Plus plan to add a custom field. Otherwise, the option will be grayed out. If you want to upgrade, you can follow the steps below.

1. Go to Settings ⚙ and then Account and settings.
2. Select the Billing & Subscription tab.
3. In the QuickBooks Online section, select Upgrade your plan.
4. Review the available plans and then select Choose plan.
5. Follow the on-screen steps to upgrade your plan.

Here's an article for your additional reference: Upgrade or downgrade your QuickBooks Online subscription. You can use the Message to customer field of your quote if you don't want to upgrade.

Feel free to visit us back if you need help along the way. Take care and have a good one!