QB Issue Resolution:

You can not.

QB is accounting and you are asking about company policy decisions.  About all you can do is print the PO, send it to each person needing to sign off on it, and when you get it back complete the order.

Resolution for Issue 'How to approve purchase invoices in the system by people outside an organisation' available: Yes (Solved).
Source: Intuit Community forum.

How to approve purchase invoices in the system by people outside an organisation: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for back complete
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for back complete [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.

Get 50% off Quickbooks Online

Click Here for 50% off!

Additional Support Options: