+    if (   $payment_received
+        && any {    ( $_->is_sales && ($_->amount < 0))
+                 || (!$_->is_sales && ($_->amount > 0))
+               } @{ $data{invoices} }) {
+      return {
+        %data,
+        result  => 'error',
+        message => $::locale->text("Received payments can only be posted for sales invoices and purchase credit notes."),
+      };
+    }
+
+    if (   $payment_sent
+        && any {    ( $_->is_sales && ($_->amount > 0))
+                 || (!$_->is_sales && ($_->amount < 0) && ($_->invoice_type eq 'purchase_invoice'))
+               } @{ $data{invoices} }) {
+      return {
+        %data,
+        result  => 'error',
+        message => $::locale->text("Sent payments can only be posted for purchase invoices and sales credit notes."),
+      };
+    }
+
+    my $max_invoices = scalar(@{ $data{invoices} });
+    my $n_invoices   = 0;
+
+    foreach my $invoice (@{ $data{invoices} }) {
+      my $source = ($data{sources} // [])->[$n_invoices];
+      my $memo   = ($data{memos}   // [])->[$n_invoices];
+
+      $n_invoices++ ;
+      # safety check invoice open
+      croak("Invoice closed. Cannot proceed.") unless ($invoice->open_amount);
+
+      if (   ($payment_sent     && $bank_transaction->not_assigned_amount >= 0)
+          || ($payment_received && $bank_transaction->not_assigned_amount <= 0)) {
+        return {
+          %data,
+          result  => 'error',
+          message => $::locale->text("A payment can only be posted for multiple invoices if the amount to post is equal to or bigger than the sum of the open amounts of the affected invoices."),
+        };
+      }
+
+      my ($payment_type, $free_skonto_amount);
+      if ( defined $::form->{invoice_skontos}->{"$bt_id"} ) {
+        $payment_type = shift(@{ $::form->{invoice_skontos}->{"$bt_id"} });
+      } else {
+        $payment_type = 'without_skonto';
+      }
+
+      if ($payment_type eq 'free_skonto') {
+        # parse user input > 0
+        if ($::form->parse_amount(\%::myconfig, $::form->{"free_skonto_amount"}->{"$bt_id"}{$invoice->id}) > 0) {
+          $free_skonto_amount = $::form->parse_amount(\%::myconfig, $::form->{"free_skonto_amount"}->{"$bt_id"}{$invoice->id});
+        } else {
+          return {
+            %data,
+            result  => 'error',
+            message => $::locale->text("Free skonto amount has to be a positive number."),
+          };
+        }
+      }
+    # pay invoice
+    # TODO rewrite this: really booked amount should be a return value of Payment.pm
+    # also this controller shouldnt care about how to calc skonto. we simply delegate the
+    # payment_type to the helper and get the corresponding bank_transaction values back
+    # hotfix to get the signs right - compare absolute values and later set the signs
+    # should be better done elsewhere - changing not_assigned_amount to abs feels seriously bogus
+
+    my $open_amount = $payment_type eq 'with_skonto_pt' ? $invoice->amount_less_skonto : $invoice->open_amount;
+    $open_amount            = abs($open_amount);
+    $open_amount           -= $free_skonto_amount if ($payment_type eq 'free_skonto');
+    my $not_assigned_amount = abs($bank_transaction->not_assigned_amount);
+    my $amount_for_booking  = ($open_amount < $not_assigned_amount) ? $open_amount : $not_assigned_amount;
+    my $amount_for_payment  = $amount_for_booking;
+
+    # get the right direction for the payment bookings (all amounts < 0 are stornos, credit notes or negative ap)
+    $amount_for_payment *= -1 if $invoice->amount < 0;
+    $free_skonto_amount *= -1 if ($free_skonto_amount && $invoice->amount < 0);
+    # get the right direction for the bank transaction
+    $amount_for_booking *= $sign;
+
+    $bank_transaction->invoice_amount($bank_transaction->invoice_amount + $amount_for_booking);
+
+    # ... and then pay the invoice
+    my @acc_ids = $invoice->pay_invoice(chart_id => $bank_transaction->local_bank_account->chart_id,
+                          trans_id      => $invoice->id,
+                          amount        => $amount_for_payment,
+                          payment_type  => $payment_type,
+                          source        => $source,
+                          memo          => $memo,
+                          skonto_amount => $free_skonto_amount,
+                          bt_id         => $bt_id,
+                          transdate     => $bank_transaction->valutadate->to_kivitendo);
+    # ... and record the origin via BankTransactionAccTrans
+    if (scalar(@acc_ids) < 2) {
+      return {
+        %data,
+        result  => 'error',
+        message => $::locale->text("Unable to book transactions for bank purpose #1", $bank_transaction->purpose),
+      };
+    }
+    foreach my $acc_trans_id (@acc_ids) {
+        my $id_type = $invoice->is_sales ? 'ar' : 'ap';
+        my  %props_acc = (
+          acc_trans_id        => $acc_trans_id,
+          bank_transaction_id => $bank_transaction->id,
+          $id_type            => $invoice->id,
+        );
+        SL::DB::BankTransactionAccTrans->new(%props_acc)->save;
+    }
+      # Record a record link from the bank transaction to the invoice
+      my %props = (