I'm here to ensure that you'll be able to send and accept receipt through emails in QuickBooks Online.
You have the option to enter multiple emails in your customer's profile or any sales transactions. Any attached email will receive the receipt once sent. Make sure that the email addresses are separated with commas (,).
Please check out the sample snips attached below on how add them on your customers profile and on sales forms:
However, if you want to receive all the receipts that were sent from your company file, make sure to set your secondary email address to have Carbon Copy (CC). This can be done from the Accounts and Settings.
To do that:
At the top right, click the Gear icon.
Select Account and Settings.
On the left pane, select Sales.
In the Messages section, you can enter the email address under Copy (Cc) new invoices to address.
From the Sales form drop-down, select Invoices and other sales forms.
You can visit these article below to learn more emailing sales forms and expense receipts in QuickBooks Online for reference:
I would also like to know if you've received any error message upon sending receipts or any exact details on what type of receipt are you working with. It will be a great help for me to narrow down this issue.
I'll be right here to help you if there's anything else you need. Thanks for coming, and stay safe.