I have mistakenly purchased the "simple start plan" but I needed the "essentials plan". Can I switch to the "Essentials Plan" just paying the extra dollars?

Yes, you can easily switch your QuickBooks Online (QBO) Simple Start plan to Essentials, and I'm here to show you how, @arg3788-gmail-co.

You'll have to consider the needs of your business in choosing the appropriate QBO plan. Since our Essentials version meets them, you can upgrade your current subscription level (Simple Start). Let's go to the Billing & Subscription menu to do this. For the detailed steps, here's how:

1. Sign in to QuickBooks Online as a primary or company admin.
2. Go to the Gear icon.
3. Select Account and settings.
4. Choose the Billing & Subscription menu.
5. In the QuickBooks Online section, select Upgrade your plan. 
6. Select Choose plan under the Essentials version. This page also indicates your rate per month. 
7. Follow the on-screen steps to upgrade your plan.

Once done, you're now ready to start using the QBO platform. To help you set up your company file, link your accounts, import your lists, set up taxes, and manage your users, I encourage you to check out this article for the complete guide: Get started with QuickBooks Online.

On top of that, I've also included this helpful reference in managing your business growth using QBO: QuickBooks Help Articles.

Stay in touch if you have other account management concerns by leaving a comment below. I'm always glad to help in any way I can.​ Take care and stay safe.

@arg3788-gmail-co 

Mind you, the discounted rate is not applicable when upgrading your plan. You can open a new blank QBO Essentials account with the discounted rate.

https://quickbooks.grsm.io/EU

then explore the Copy feature to clone your data from old account.

https://rewindio.grsm.io/quickbooks