It's great to see you here in the Community today, @Ejin.
Thanks for choosing QuickBooks to cater your business needs. I'll provide some information about the availability of the supplier payment feature in QuickBooks Online (QBO).
You're correct that you can't utilize the supplier payment option in a QBO Simple Start subscription. You'll have to upgrade to a QBO Essentials or Plus subscription to utilize the feature.
In case you really need this feature and you want to upgrade your subscription, then you can follow the steps:
Go to the Gear icon and then select the Account and settings.
Click the Billing & Subscription tab.
In the QBO section, select Upgrade your plan.
Review the available plans and then select Choose plan.
If you need any resources that you may bookmark for future use, go to our QuickBooks Online Help page. On the site, you may find a variety of support articles and even video tutorials to aid you with your QBO tasks.
Let me know how it goes by dropping a comment below. I'll be more than happy to help you and make your QuickBooks experience awesome. Take care!