Hello there, Vraiteri. I'll provide a way to add the CPT codes so patients have the necessary info to submit to insurers.
In QuickBooks Online, CPT codes added as items or included solely in the line item details will not appear on customer statements. The Statements feature summarizes invoice balances, including dates of service, descriptions, and amounts. However, it doesn't display line-level details, such as CPT codes, and it functions as designed in the software.
Alternatively, we can manually add the CPT service codes in the Description or in the Memo on Statement (hidden) section of the invoice to ensure they appear on customer statements.
See screenshots below:

Additionally, we can download and print a PDF file for your patients, so they can submit a copy to their insurance company. See screenshot below to download a statement:

Please let me know if you have any other concerns regarding this topic, Vraiteri.