It's nice to see you here, JulioS.

We can perform some basic troubleshooting steps to fix this. It could be that the stored cache in the system is the reason why a payment link on pdf invoices is not showing.

Let's start with accessing your QuickBooks account through a private browsing window. This will help us determine if this is a browser-related issue since this mode doesn't save site data and cache files. 

Here are the shortcut keyboards:
 

• Ctrl + Shift + N for Google Chrome
• Ctrl + Shift + P for Firefox & Microsoft Edge
• Command + Shift + N for Safari

If it works, we'll have to go back to your normal browser and perform a clear cache to clean up your system. Doing this process will also enhance your browsing experience.  Alternatively, you can use other supported browsers to further isolate the issue.

For reference about creating invoices, you can check this article: Create invoices in QuickBooks Online. 

Need help categorizing your income and expense bank transactions? This article can help you with the process: Categorize and match online bank transactions in QuickBooks Online.

If you need to learn more about processing invoices and payments in QuickBooks, please let me know. I'd be happy to address your concerns. If you want to complete other tasks, lay down the details and I'll help you out.