City of Dallas I paid for parking and have proof and they are still telling me to pay Dallas Texas

Since you are in law enforcement, you should be well aware that just having your card charged is NOT proof that you paid for parking for THAT vehicle at THAT time.

I have used these apps before at other lots(in my city), and one thing they always require is the License Plate Number and location.  All your deduction from your account shows is that you paid something to this company.  There is not a specific time you paid for, nor a specific vehicle.  For all they know you could have parked 2 cars, paid for 1 and are trying to get out of paying for both.  I am not saying you did this, but with what you have there is nothing to say that isn't the case. 

If you want REAL proof, you need to go back to the App and request a receipt.  The receipt from that company will show the License Plate you paid for, the time you paid for it, and how long you paid for.  IF once you get this receipt it shows you received a ticket during the time you had paid for, you have a valid complaint and the ticket should be removed.  However, if you find you did something such as enter the wrong license plate, wrong location, or didn't pay for enough time(such as you paid through 2PM and the ticket was written at 2:05PM) then the ticket is valid and you need to pay it.

By the way since you are in law enforcement, let me give you another thing to think about from your statement about you jepopardizing your carear over $5....How come people shoplift a $5 item when they have $40 in their purse/wallet?  Not that I am equating not paying for parking to shoplifting(although they are both forms of theft), but the answer to both is the same.  Sometimes people just don't think.