The sad truth is that the majority of your colleagues would throw you under the bus to save their job, reputation, etc.
My personal goal is to work in a manner that is beyond reproach so when these situations occur and other people get involved to review it then it is clear where the fault lies. This seems to be true in your case if you have written confirmation from your colleague about paying the invoice.
As shitty as it is, I guess you would need to escalate the issue to get a desired resolution.
BTW, any updates on the outcome?
!BEER
Well I went to the boss and he was willing to allow the department to pay. So he called the lab and explained everything. We are waiting on them to send us a new invoice so we can transfer the money.
The guy that messed up was called in. Don't know what happened there, but I do know they address his multiple little slip ups that he keeps ignoring and blaming on others.
So as of now, nothing has been payed, from my side or the department, but the lab is aware of the situation and my name is clear 😅
Ah, well, at least it's something :D
Hope it turns out well with the finances and you have minimal contact with your accident-prone colleague :D
!LUV
!LUV