I can see how you want to use Google Calendar in your invoice. I'll provide you with the easiest way so you'll be able to use this in the future, Default.
This integration feature has been favorable to some of the customers who find Google Calendar useful for their invoices. Therefore, some already sent feedback to make this possible. If this happens, you can go to the Customer Feedback page and search for this request so you can cast your vote. This will be the most effective way for the feature to be brought to product developers' attention. I've added a screenshot for a visual guide:
Sample Only:
On the other hand, if you're unable to find a related request on this, I recommend sending feedback to let our product team know how this is helpful for your business. To do so, follow the steps outlined below:
This goes to our Product Development team to help improve your experience in QuickBooks Online.
In addition, after creating an invoice, learn how you can receive and process payments online. Read this article for more information and detailed steps: Receive And Process Payments in QuickBooks With QuickBooks Payments.
You can always post your comment below if you have further questions about invoice integration with Google Calendar with the new layout. We're always right here to assist.