You don't seem to get that the money is spent when Congress allocates it, not when a public servant puts it on a credit card. You want accountability talk to your representative.

This will just make government less efficient as it goes through extra steps to request invoices and post payment, or perhaps even spending petty cash.

It will exclude government from buying certain products where this isn't possible.

Of course this is all quite irrelevant, since it's a publicity stunt for the people who are not interested in saving taxpayer money but hating and destroying.