diff --git a/models/account_payment.py b/models/account_payment.py
index bf7d2c0..7975908 100644
--- a/models/account_payment.py
+++ b/models/account_payment.py
@@ -143,7 +143,10 @@ class AccountPayment(models.Model):
                 # This module creates additional lines that don't fit the standard pattern
                 has_substract = hasattr(pay, 'amount_substract') and pay.amount_substract and pay.amount_substract > 0
                 
-                if not has_substract:
+                # POS Combination Payments can have multiple liquidity lines
+                is_pos_payment = pay._context.get('pos_payment')
+
+                if not has_substract and not is_pos_payment:
                     if len(liquidity_lines) != 1:
                         raise UserError(_(
                             "Journal Entry %s is not valid. In order to proceed, the journal items must "
@@ -175,24 +178,34 @@ class AccountPayment(models.Model):
                         move.display_name,
                     ))
 
-                if counterpart_lines.account_id.account_type == 'asset_receivable':
-                    partner_type = 'customer'
+                if counterpart_lines:
+                    account_type = counterpart_lines[0].account_id.account_type
+                    if account_type == 'asset_receivable':
+                        partner_type = 'customer'
+                    elif account_type == 'liability_payable':
+                        partner_type = 'supplier'
+                    else:
+                        partner_type = 'customer' if pay.payment_type == 'inbound' else 'supplier'
                 else:
-                    partner_type = 'supplier'
+                    partner_type = 'customer' if pay.payment_type == 'inbound' else 'supplier'
 
-                liquidity_amount = liquidity_lines.amount_currency
+                liquidity_amount = sum(liquidity_lines.mapped('amount_currency')) if len(liquidity_lines) > 1 else liquidity_lines.amount_currency
 
-                move_vals_to_write.update({
-                    'currency_id': liquidity_lines.currency_id.id,
-                    'partner_id': liquidity_lines.partner_id.id,
-                })
-                payment_vals_to_write.update({
-                    'amount': abs(liquidity_amount),
-                    'partner_type': partner_type,
-                    'currency_id': liquidity_lines.currency_id.id,
-                    'destination_account_id': counterpart_lines.account_id.id,
-                    'partner_id': liquidity_lines.partner_id.id,
-                })
+                # Use the first line for currency and partner if multiple
+                first_liquidity_line = liquidity_lines[0] if len(liquidity_lines) > 0 else liquidity_lines
+                
+                if first_liquidity_line:
+                    move_vals_to_write.update({
+                        'currency_id': first_liquidity_line.currency_id.id,
+                        'partner_id': first_liquidity_line.partner_id.id,
+                    })
+                    payment_vals_to_write.update({
+                        'amount': abs(liquidity_amount),
+                        'partner_type': partner_type,
+                        'currency_id': first_liquidity_line.currency_id.id,
+                        'destination_account_id': counterpart_lines[0].account_id.id if counterpart_lines else False,
+                        'partner_id': first_liquidity_line.partner_id.id,
+                    })
                 if liquidity_amount > 0.0:
                     payment_vals_to_write.update({'payment_type': 'inbound'})
                 elif liquidity_amount < 0.0:
@@ -213,7 +226,21 @@ class AccountPayment(models.Model):
                     pay.outstanding_account_id = pay.journal_id.default_account_id
                 else:
                     # Fallback to the original logic if no default account is set
-                    pay.outstanding_account_id = pay._get_outstanding_account(pay.payment_type)
+                    if pay.payment_type == 'inbound':
+                        pay.outstanding_account_id = (pay.payment_method_line_id.payment_account_id
+                                                      or pay.journal_id.default_account_id)
+                    elif pay.payment_type == 'outbound':
+                        pay.outstanding_account_id = (pay.payment_method_line_id.payment_account_id
+                                                      or pay.journal_id.default_account_id)
+                    else:
+                        pay.outstanding_account_id = False
             else:
                 # For bank/cash journals, use the original logic
-                pay.outstanding_account_id = pay._get_outstanding_account(pay.payment_type)
\ No newline at end of file
+                if pay.payment_type == 'inbound':
+                    pay.outstanding_account_id = (pay.payment_method_line_id.payment_account_id
+                                                  or pay.journal_id.default_account_id)
+                elif pay.payment_type == 'outbound':
+                    pay.outstanding_account_id = (pay.payment_method_line_id.payment_account_id
+                                                  or pay.journal_id.default_account_id)
+                else:
+                    pay.outstanding_account_id = False
\ No newline at end of file