How to add Store Name or website url to paypal express checkout

Currently using zencart 1.5.7C and paypal express checkout

I have several websites (all use paypal express checkout) and use a single paypal account.

I can't tell the order from which website when I got the paypal payment notification email.

The content in the payment notification email I received from paypal mainly includes:
item name+attribute+item number
I want to add the website name (STORE_NAME), for example, change the item number to STORE_NAME+item number.

So how to achieve this purpose?

Thank you!

The transaction data sent to PayPal includes the store name in the "Invoice Number" field (not the "order number", not the "transaction number").
It's "customer ID" + "current time" + "store name":

https://github.com/zencart/zencart/blob/v157/includes/modules/payment/paypalwpp.php#L395-L396

Thank you.
I see now.
Because the two domains of my sites are similar, and the store name(domain) has been cut and replaced, so I did not recognize it.