Getting "Integrity constraint violation (Duplicate entry for key)" in Laravel - php

Question

I have a table that I have recently edited to add another index using two columns (which combined are required to be unique).
The problem is now I get an error when I go to create a new model record:
Integrity constraint violation: 1062 Duplicate entry ... for key ....
The two columns are titled:
shipment_origin
pro_number
So as an example, the end result would look like: 1-230185
And I have checked, the record is created technically, it just doesn't follow through and the error is returned. So to make it simple, there is no record before hand (so there's no duplicate entry), a record is created in the database and the error is returned (no matter what).
Or is there a way to go about doing this directly through Laravel rather than MySQL?
Update
Here is the public function in my controller:
public function store(Request $request)
{
$this->validate(request(), [
'pro_number' => 'required',
'shipment_origin' => 'required'
/*'piecesNumber' => 'required' (had to remove for now, but must review)*/
]);
$user_id = Auth::id();
$input = $request->all();
//Save Initial Shipment Data
$shipment = new Shipment();
$shipment->pro_number = request('pro_number');
$shipment->shipment_origin = request('shipment_origin');
$shipment->date = request('date');
$shipment->due_date = request('due_date');
$shipment->tractor_id = request('tractor_id');
$shipment->trailer_id = request('trailer_id');
$shipment->driver_id = request('driver_id');
$shipment->notes = request('notes');
$shipment->shipper_no = request('shipper_no');
$shipment->ship_to = request('ship_to');
$shipment->ship_from = request('ship_from');
$shipment->bill_to = request('bill_to');
$shipment->bill_type = request('bill_type');
$shipment->load_date = request('load_date');
$shipment->shipment_status = 1;
$shipment->shipment_billing_status = (isset($request->shipment_billing_status) && !empty($request->shipment_billing_status)) ? $request->shipment_billing_status : 1;
$shipment->created_by = $user_id;
$shipment->cn_billtoName = request('cn_billtoName');
$shipment->cn_billtoAddress1 = request('cn_billtoAddress1');
$shipment->cn_billtoAddress2 = request('cn_billtoAddress2');
$shipment->cn_billtoCity = request('cn_billtoCity');
$shipment->cn_billtoState = request('cn_billtoState');
$shipment->cn_billtoZip = request('cn_billtoZip');
$shipment->cn_billtoEmail = request('cn_billtoEmail');
$shipment->cn_billtoPhone = request('cn_billtoPhone');
$shipment->cn_shiptoName = request('cn_shiptoName');
$shipment->cn_shiptoAddress1 = request('cn_shiptoAddress1');
$shipment->cn_shiptoAddress2 = request('cn_shiptoAddress2');
$shipment->cn_shiptoCity = request('cn_shiptoCity');
$shipment->cn_shiptoState = request('cn_shiptoState');
$shipment->cn_shiptoZip = request('cn_shiptoZip');
$shipment->cn_shiptoEmail = request('cn_shiptoEmail');
$shipment->cn_shiptoPhone = request('cn_shiptoPhone');
$shipment->cn_shipfromName = request('cn_shipfromName');
$shipment->cn_shipfromAddress1 = request('cn_shipfromAddress1');
$shipment->cn_shipfromAddress2 = request('cn_shipfromAddress2');
$shipment->cn_shipfromCity = request('cn_shipfromCity');
$shipment->cn_shipfromState = request('cn_shipfromState');
$shipment->cn_shipfromZip = request('cn_shipfromZip');
$shipment->cn_shipfromEmail = request('cn_shipfromEmail');
$shipment->cn_shipfromPhone = request('cn_shipfromPhone');
$shipment->fuelChargeDesc = request('fuelChargeDesc');
$shipment->fuelChargeAmt = request('fuelChargeAmt');
$shipment->fuelChargeTotal = request('fuelChargeTotal');
$shipment->permitChargeDesc = request('permitChargeDesc');
$shipment->permitChargeAmt = request('permitChargeAmt');
$shipment->permitChargeTotal = request('permitChargeTotal');
$shipment->otherChargeDesc = request('otherChargeDesc');
$shipment->otherChargeAmt = request('otherChargeAmt');
$shipment->otherChargeTotal = request('otherChargeTotal');
$shipment->noCharge = request('noCharge');
$shipment->noSettle = request('noSettle');
$shipment->Total = request('Total');
if ((request('shipment_billing_status') == 2) || (request('shipment_billing_status') == 3)){
$balance = 0.00;
}else{
$balance = request('Total');
}
$shipment->Balance = $balance;
$shipment->freightBillSubtotal = request('freightBillSubtotal');
$shipment->save();
//Save Shipment Details
for ($i = 0; $i < count($request->shipment_details['piecesNumber']); $i++) {
//the first line used to be 'shipment_id' => $shipment->pro_number,
Shipment_Detail::create([
'shipmentID' => $shipment->id,
'pieces_number' => $request->shipment_details['piecesNumber'][$i],
'pieces_type' => $request->shipment_details['piecesType'][$i],
'rate_type' => $request->shipment_details['rateType'][$i],
'charge' => $request->shipment_details['charge'][$i],
'weight' => $request->shipment_details['weight'][$i],
'hazmat' => $request->shipment_details['hazmat'][$i],
'description' => $request->shipment_details['description'][$i] ]);
}
$carrier = \App\Customer::where('carrier','=',1)->get();
foreach($carrier as $car){
$carrierUsers = $car->users;
if ($carrierUsers->count() > 0){
foreach($carrierUsers as $carrierUser){
$carrierUser->notify(new FreightBillNew($shipment));
}
}
}
Session::flash('success_message','Freight Bill Successfully Created'); //<--FLASH MESSAGE
//Return to Register//
return redirect('/shipments/accounts');
}