Iterating through a list, but can't access distinct item values

I am building invoices with PDFsharp.

This is my SQL table (tblTripsPerMonth):

I've bound it to an ObservableCollection (PaidTrips).

The goal is to create one (1) PDF for each distinct "CompanyName" in the LicenseHolderID column. To achieve this, I convert to a List, and group by LicenseHolderID.

var paidTrips = PaidTrips
    .GroupBy(p => new {
        p.LicenseHolderID
})
.ToList();

After that, I iterate over the list with a foreach-loop:

foreach (var trip in paidTrips) {
    
    // I grab the distinct name
    string licenseholder = trip.Key.LicenseHolderID.ToString();
    
    // I summarize many of the columns
    decimal totalPayment = trip.Sum(x => x.Payment);
    decimal totalPaymentNet = trip.Sum(x => x.Payment);
    decimal totalOrderFee = trip.Sum(x => x.Payment);
    decimal totalPaymentFee = trip.Sum(x => x.Payment);
    
    // I grab the first value of some other columns, which won't change
    string licenseholderInvoiceID = trip.Select(x => x.LicenseHolderInvoiceID).FirstOrDefault().ToString();
    string ridelRegionInvoiceID = trip.Select(x => x.RidelRegionInvoiceID ).FirstOrDefault().ToString();

// Creating PDF document using PDFsharp:
// PDFsharp code
// PDFsharp code
// PDFsharp code
}

I am able to create a PDF-document, one for each distinct LicenseHolderID, by adding the licenseHolderID-string to the file-path of PDFsharps document.Save().

But I am not able to fill the PDF-document with all the information I need. I have the summarized amounts - good, because I absolutely need to display the full invoice amount. But -- I also need to go into detail. I do not have amounts per VehicleID.

For "CompanyName1", that'd be AG4203000002 and AG4203000003, with their corresponding row data.

I did do this...

IEnumerable<string> vehicleIds = trip
    .Select(x => x.VehicleID)
    .Distinct()
    .ToArray();
string vehicle = string.Join(", ", vehicleIds);

...in order to separate the VehicleID distinct values from eachother. I then put the string vehicle into PDFsharps way of drawing text onto the PDF (DrawString):

gfx.DrawString(vehicle, /* font and color customization */);

Which gives me the correct amount of VehicleID for each LicenseHolderID, but in one, long string... Not optimal.

Which brings me to my question: A): I need to bring along the row data of the other columns pertaining to the distinct vehicles in VehicleID, so that I can fill in details in my PDFs, and not just the summarized values, and B): if the solution to A) involves getting rid of the long, hacky string (vehicle), that'd be optimal, if not - that's okay too.

UPDATE (adding code from @Dai's answer):

// PaidTrip = My holder class, which I've bound to a ObservableCollection (PaidTrips)
var paidTrips = PaidTrips.ToList(); // I was unsure about this one
IEnumerable<IGrouping<String, PaidTrip>> tripsGroupedByCompany = paidTrips.GroupBy(pt => pt.LicenseHolderID);

foreach (IGrouping<String, PaidTrip>> companyGroup in tripsGroupedByCompany) {
    
    string licenseHolderId = companyGroup.Key;
    gfx.DrawString(/* code goes foo */);

    // I tried adding Key here, but that gave me a squiggly under "t.VehicleID"
    var groupedByVehicle = companyGroup.GroupBy(t => t.VehicleID);
    
    foreach (IGrouping<String, PaidTrip> vehicleGroup in groupedByVehicle) {

        // This is where I get a red squiggly; under Key
        String vehicleId = groupedByVehicle.Key;

        gfx.DrawString(/* code goes foo */);
        
        foreach (PaidTrip trip in vehicleGroup) {
      
            gfx.DrawString(/* code goes foo */);
        }
    }
}

This is the error:

CS1061: IEnumerable<IGrouping<string, PaidTrip>> does not contain a definition for 'Key' and no accessible extension method 'Key' accepting a first argument of type 'IEnumerable<IGrouping<string, PaidTrip>>' could be found (are you missing a using directive or an assembly reference?)