I've got your back, Pinar. Let me help you ensure the currency appears when printing your refund receipt in QuickBooks Online (QBO).

When you say return receipts, are you referring to the refund receipt feature in QBO? If so, I'd be glad to provide some solutions to make sure the currency shows up when printing your refund receipts. 

Let's customise your Default Standard template to show the currency when previewing or printing the PDF of your refund receipts. To guide you further, please follow the steps below:

1.  Go to Settings and then tap Custom form styles.
2. Click the Edit button in the Standard template.
   
   
3. From the Design tab, select Change up the template.
4. Choose a layout except for the Airy New template.
   

Furthermore, you can also add a (€) sign to your template by following the steps below:
 

1. Select the Content tab from the standard template.
2. Choose the Table section, then click Edit labels and widths.
3. Add a (€) sign beside the Rate and Amount sections.
   

Here's a sample result of how it appears in your PDF:

However, please provide additional details if this isn't the case and you mean something else with the return receipts.

In addition to this, you can visit these articles for further instructions on how to include additional details or personalize sales transactions:

• Add, customise, or remove logos on sales forms
• Customise invoices, estimates, and sales receipts in QuickBooks Online

Please keep me updated on how these steps turn out, and let me know if you have any other concerns by commenting below. Have a great day ahead!