Is there a proper way to manage the "DocNumber"

In my app, i create invoices using the PHP SDK. Then, I add those invoices to my QuickBooks company. The issue i face is how to properly populate the 'DocNumber' field. Since those must be unique i initially thought of simply using the id of the invoice which works great.... Until you manually add invoices in QuickBooks and enter a DocNumber other than the ID.

For example, if the ID is 10, but i enter 15 as the DocNumber, when i will enventually transferts an invoice from my app with the ID 15, it will fail to set the DocNumber to 15 because it would already be in use.

Is there any simple way to prevent this kind of issue?

Thank you