Hope you're doing fine, happyjacks!

Yes, you're right that QuickBooks Online don't have an  option to memorize transaction. You only need to create a recurring transaction for an invoice.

 I'll walk you through on how you can create a recurring invoices.

1. Go to the Gear icon. 
2. Select Recurring transactions under the Lists column.
3. Click New.
   
4. Select the type of transaction to create (invoice), and then select OK.
   
5. Enter a Template name.
6. Select a Type: Scheduled.
   

For additional details, you can check these articles:

• Create recurring transactions in QuickBooks Online.
• Edit a recurring template

Please know that I'm always here if you ever need anything else with QuickBooks, happyjacks. Take care and stay safe always.