diff --git a/Marco.Pms.Services/Controllers/CollectionController.cs b/Marco.Pms.Services/Controllers/CollectionController.cs
index f4f908b..4664700 100644
--- a/Marco.Pms.Services/Controllers/CollectionController.cs
+++ b/Marco.Pms.Services/Controllers/CollectionController.cs
@@ -307,7 +307,7 @@ namespace Marco.Pms.Services.Controllers
             response.CreatedBy = _mapper.Map<BasicEmployeeVM>(loggedInEmployee);
             response.BalanceAmount = response.BasicAmount + response.TaxAmount;
 
-            return Ok(ApiResponse<object>.SuccessResponse(response, "Invoice Created Successfully", 201));
+            return StatusCode(201, ApiResponse<object>.SuccessResponse(response, "Invoice Created Successfully", 201));
         }
 
         /// <summary>
@@ -387,7 +387,7 @@ namespace Marco.Pms.Services.Controllers
                 _logger.LogInfo("Successfully created received payment {PaymentId} for invoice {InvoiceId}",
                     receivedInvoicePayment.Id, model.InvoiceId);
 
-                return Ok(ApiResponse<object>.SuccessResponse(response, "Payment invoice received successfully", 201));
+                return StatusCode(201, ApiResponse<object>.SuccessResponse(response, "Payment invoice received successfully", 201));
             }
             catch (Exception ex)
             {
@@ -398,5 +398,61 @@ namespace Marco.Pms.Services.Controllers
             }
         }
 
+        /// <summary>
+        /// Marks the specified invoice as completed if it exists and is not already completed.
+        /// </summary>
+        /// <param name="invoiceId">The unique identifier of the invoice to mark as completed.</param>
+        /// <returns>An action result indicating success or the nature of the error.</returns>
+
+        [HttpPut("invoice/marked/completed/{invoiceId}")]
+        public async Task<IActionResult> MarkAsCompletedAsync(Guid invoiceId)
+        {
+            // Create a new async database context for the current request's scope.
+            await using var _context = await _dbContextFactory.CreateDbContextAsync();
+
+            // Retrieve the current logged in employee for audit/logging (optional use).
+            var loggedInEmployee = await _userHelper.GetCurrentEmployeeAsync();
+
+            // Attempt to find the invoice with tenant isolation; use AsNoTracking if no updates needed (but here we update so tracking is okay).
+            var invoice = await _context.Invoices
+                .FirstOrDefaultAsync(i => i.Id == invoiceId && i.TenantId == tenantId);
+
+            // Log and return 404 if the invoice does not exist.
+            if (invoice == null)
+            {
+                _logger.LogWarning("Invoice not found for ID {InvoiceId} and TenantId {TenantId}", invoiceId, tenantId);
+                return NotFound(ApiResponse<object>.ErrorResponse("Invoice not found", "The specified invoice does not exist", 404));
+            }
+
+            // If the invoice is already marked as completed, log and return meaningful error.
+            if (invoice.MarkAsCompleted)
+            {
+                _logger.LogWarning("Attempt to mark already completed invoice {InvoiceId} as completed by user {UserId}", invoiceId, loggedInEmployee.Id);
+                return BadRequest(ApiResponse<object>.ErrorResponse(
+                    "Invoice already completed",
+                    "Invoice is already marked as completed", 400));
+            }
+
+            try
+            {
+                // Mark invoice as completed.
+                invoice.MarkAsCompleted = true;
+
+                // Persist the change to the database.
+                await _context.SaveChangesAsync();
+
+                _logger.LogInfo("Invoice {InvoiceId} marked as completed by user {UserId}", invoiceId, loggedInEmployee.Id);
+
+                return Ok(ApiResponse<object>.SuccessResponse(new { }, "Invoice is marked as completed successfully", 200));
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Error occurred while marking invoice {InvoiceId} as completed by user {UserId}", invoiceId, loggedInEmployee.Id);
+                return StatusCode(500, ApiResponse<object>.ErrorResponse(
+                    "Internal server error",
+                    "An unexpected error occurred while processing the request", 500));
+            }
+        }
+
     }
 }