Some background info:
https://perishablepress.com/tell-google-to-not-index-certain-parts-of-your-page/
Make a robots.txt file and include your invoiceplane directory (or if you use a subdomain, include the whole site)
User-agent: *
Disallow: /
Disallow: /invoiceplane/
Disallow: /uploads/
Also…
Add the following link at the start of your invoice template
<!--googleoff: all-->
and this at the end
<!--googleon: all>