My recommendation: Send an escalation to Aaron Patel (Joe's manager and your CISO/Treasury lead, who has approval authority at this threshold). Concurrently, open a ServiceNow ticket to fix the broken delegation rule so this doesn't recur during Joe's remaining PTO days.
I have drafted the escalation and the ticket. Both await your one-click confirmation. I will not approve the PO in Fusion myself — that authority stays with Aaron (or Joe when he returns).