diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
index 46d8095..54fad99 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
@@ -55,6 +55,9 @@ public abstract class ChannelBase implements Observable {
 
     public boolean tick() {
         requirements.forEach(Requirement::tick);
+        try {
+            requirements.stream().filter(r -> r.getTTL() == 0).forEach(re -> re.getCreator().getProductFromStorage(re.getProductName(), re.getProductType()).setStateToAvailable());
+        } catch (Exception ignored) {}
         requirements = requirements.stream().filter(r -> r.getTTL() > 0).collect(Collectors.toCollection(LinkedList::new));
         notifyAllObservers();
         return requirements.size() != 0;
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/base/NodeBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/base/NodeBase.java
index 08f340c..8db8843 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/base/NodeBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/base/NodeBase.java
@@ -15,16 +15,14 @@ import org.javamoney.moneta.Money;
 
 import javax.money.MonetaryAmount;
 import javax.naming.InsufficientResourcesException;
-import java.util.HashMap;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 
 public class NodeBase implements ChannelObserver {
     private final Map<ChannelBase, ChannelSubscriptionType> subscribedChannels;
     private final List<Product> products;
     private final List<Transaction> refusedTransactions;
+    private final List<RefusedRequirement> refusedRequirements;
 
     private MonetaryAmount money;
 
@@ -37,6 +35,7 @@ public class NodeBase implements ChannelObserver {
         this.subscribedChannels = new HashMap<>();
         this.products = new LinkedList<>();
         this.refusedTransactions = new LinkedList<>();
+        this.refusedRequirements = new LinkedList<>();
         this.money = Money.of(0, "USD");
     }
 
@@ -44,6 +43,7 @@ public class NodeBase implements ChannelObserver {
         this.subscribedChannels = new HashMap<>();
         this.products = new LinkedList<>();
         this.refusedTransactions = new LinkedList<>();
+        this.refusedRequirements = new LinkedList<>();
         this.money = Money.of(m, "USD");
     }
 
@@ -55,7 +55,7 @@ public class NodeBase implements ChannelObserver {
                     .filter(ch -> ch.getProductType().equals(product.getProductType()))
                     .findAny().ifPresent(channel -> channel.addTransaction(transaction));
         } catch (InsufficientResourcesException e) {
-            e.printStackTrace();
+            System.err.println(e.getMessage());
         }
     }
 
@@ -67,7 +67,7 @@ public class NodeBase implements ChannelObserver {
                     .filter(ch -> ch.getProductType().equals(prevTransaction.getProduct().getProductType()))
                     .findAny().ifPresent(channel -> channel.addTransaction(transaction));
         } catch (InsufficientResourcesException e) {
-            e.printStackTrace();
+            System.err.println(e.getMessage());
         }
     }
 
@@ -124,6 +124,16 @@ public class NodeBase implements ChannelObserver {
                 price = getProductFromStorage(pName, pType).getPrice();
             }
             catch (NullPointerException e) {
+                refusedRequirements.add(new RefusedRequirement(tType, pType, pName, price));
+                throw new InsufficientResourcesException("product unavailable");
+            }
+        }
+        if (tType == TransactionType.SALE) {
+            try {
+                getProductFromStorage(pName, pType).setStateToInRequirement();
+            }
+            catch (NullPointerException | IllegalStateException e) {
+                refusedRequirements.add(new RefusedRequirement(tType, pType, pName, price));
                 throw new InsufficientResourcesException("product unavailable");
             }
         }
@@ -239,9 +249,10 @@ public class NodeBase implements ChannelObserver {
     }
 
     boolean requirementCheck(Requirement req) {
+        Product product = getProductFromStorage(req.getProductName(), req.getProductType());
         return (req.getTransactionType() == TransactionType.SALE && money.isGreaterThanOrEqualTo(req.getPrice())) ||
-                (req.getTransactionType() == TransactionType.PURCHASE && getProductFromStorage(req.getProductName(), req.getProductType()) != null &&
-                        getProductFromStorage(req.getProductName(), req.getProductType()).getProductState() == ProductState.AVAILABLE);
+                (req.getTransactionType() == TransactionType.PURCHASE && product != null &&
+                        ((product.getProductState() == ProductState.AVAILABLE) || product.getProductState() == ProductState.IN_REQUIREMENT));
     }
 
     @Override
@@ -261,3 +272,17 @@ public class NodeBase implements ChannelObserver {
         //System.out.println(this.getClass().getSimpleName() + ": " + money.getNumber());
     }
 }
+
+class RefusedRequirement {
+    public final TransactionType tType;
+    public final ProductType pType;
+    public final String pName;
+    public final MonetaryAmount price;
+
+    public RefusedRequirement(TransactionType tType, ProductType pType, String pName, MonetaryAmount price) {
+        this.tType = tType;
+        this.pType = pType;
+        this.pName = pName;
+        this.price = price;
+    }
+}
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/ProductTransaction.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/ProductTransaction.java
index 640ca63..68c5b69 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/ProductTransaction.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/ProductTransaction.java
@@ -17,7 +17,7 @@ public class ProductTransaction extends Transaction {
         this.product = product;
         type = null;
         lastOperation = product.getCurrentOperation();
-        if (product == null || product.getProductState() != ProductState.AVAILABLE) throw new InsufficientResourcesException("product not available");
+        if (product == null || product.getProductState() != ProductState.IN_REQUIREMENT) throw new InsufficientResourcesException("product unavailable");
         product.setCurrentOperation(this);
         product.setStateToReadyForDispatch();
         creator.getStorage().remove(product);
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/Product.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/Product.java
index 6252afd..b556cb1 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/Product.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/Product.java
@@ -71,22 +71,27 @@ public class Product
     // "State machine methods"
 
     /**
-     * Set current product state to AVAILABLE
+     * Set current product state to AVAILABLE. Throws IllegalStateException if the product is not IN_ACTION, READY_FOR_RECEPTION or IN_REQUIREMENT.
      */
     public void setStateToAvailable()
     {
-        this.productState = ProductState.AVAILABLE;
+        if (this.productState.equals(ProductState.IN_ACTION) ||
+                this.productState.equals(ProductState.READY_FOR_RECEPTION) ||
+                this.productState.equals(ProductState.IN_REQUIREMENT))
+            this.productState = ProductState.AVAILABLE;
+        else
+            throw new IllegalStateException("Cannot set state AVAILABLE. Product is not IN_ACTION, READY_FOR_RECEPTION or IN_REQUIREMENT");
     }
 
     /**
-     * Set current product state to READY_FOR_DISPATCH. Throws IllegalStateException if the product is not AVAILABLE.
+     * Set current product state to READY_FOR_DISPATCH. Throws IllegalStateException if the product is not IN_REQUIREMENT.
      */
     public void setStateToReadyForDispatch()
     {
-        if(this.productState.equals(ProductState.AVAILABLE))
+        if(this.productState.equals(ProductState.IN_REQUIREMENT))
             this.productState = ProductState.READY_FOR_DISPATCH;
         else
-            throw new IllegalStateException("Cannot set state READY_FOR_DISPATCH. Product is not AVAILABLE!");
+            throw new IllegalStateException("Cannot set state READY_FOR_DISPATCH. Product is not IN_REQUIREMENT!");
     }
 
     /**
@@ -122,6 +127,17 @@ public class Product
             throw new IllegalStateException("Cannot set state IN_ACTION. Product is not AVAILABLE!");
     }
 
+    /**
+     * Set current product state to IN_REQUIREMENT. Throws IllegalStateException if the product is not AVAILABLE.
+     */
+    public void setStateToInRequirement()
+    {
+        if(this.productState.equals(ProductState.AVAILABLE))
+            this.productState = ProductState.IN_REQUIREMENT;
+        else
+            throw new IllegalStateException("Cannot set state IN_REQUIREMENT. Product is not AVAILABLE!");
+    }
+
     /*
     public void setProductState(ProductState productState)
     {
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
index 906282e..7e4be38 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
@@ -2,5 +2,5 @@ package cz.cvut.fel.sit.omo.foodchain.product;
 
 public enum ProductState
 {
-    AVAILABLE, READY_FOR_DISPATCH, IN_TRANSIT, READY_FOR_RECEPTION, IN_ACTION
+    AVAILABLE, READY_FOR_DISPATCH, IN_TRANSIT, READY_FOR_RECEPTION, IN_ACTION, IN_REQUIREMENT
 }