diff --git a/QRBee.Core/ClientCardData.cs b/QRBee.Core/ClientCardData.cs
new file mode 100644
index 0000000..f5c180e
--- /dev/null
+++ b/QRBee.Core/ClientCardData.cs
@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace QRBee.Core
+{
+    public class ClientCardData
+    {
+
+        public string CardNumber
+        {
+            get;
+            init;
+        }
+
+        public string ExpirationDateMMYY
+        {
+            get;
+            init;
+        }
+
+        public string? ValidFrom
+        {
+            get;
+            set;
+        }
+
+        public string CardHolderName
+        {
+            get;
+            init;
+        }
+
+        public string CVC
+        {
+            get;
+            init;
+        }
+
+        public int? IssueNo
+        {
+            get;
+            set;
+        }
+
+        public string AsString() => $"{CardNumber}|{ExpirationDateMMYY}|{ValidFrom}|{CardHolderName}|{CVC}|{IssueNo}";
+
+    }
+}
diff --git a/QRBee.Core/Data/ClientToMerchantResponse.cs b/QRBee.Core/Data/ClientToMerchantResponse.cs
new file mode 100644
index 0000000..64e762b
--- /dev/null
+++ b/QRBee.Core/Data/ClientToMerchantResponse.cs
@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace QRBee.Core.Data
+{
+    public record ClientToMerchantResponse
+    {
+        public MerchantToClientRequest Request
+        {
+            get;
+            init;
+        }
+
+        public string ClientId
+        {
+            get;
+            init;
+        }
+
+        public DateTime TimeStampUTC
+        {
+            get;
+            init;
+        }
+
+        public string? ClientSignature
+        {
+            get;
+            set;
+        }
+
+        public string EncryptedClientCardData
+        {
+            get;
+            init;
+        }
+
+        public string AsString() => $"{Request.AsString()}|{ClientId}|{TimeStampUTC:O}";
+
+    }
+}
diff --git a/QRBee.Core/Data/MerchantToClientRequest.cs b/QRBee.Core/Data/MerchantToClientRequest.cs
new file mode 100644
index 0000000..8176107
--- /dev/null
+++ b/QRBee.Core/Data/MerchantToClientRequest.cs
@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace QRBee.Core.Data
+{
+    public record MerchantToClientRequest
+    {
+        public string TransactionId
+        {
+            get;
+            init;
+        }
+
+        public string Name
+        {
+            get;
+            init;
+        }
+
+        public decimal Amount
+        {
+            get;
+            init;
+        }
+
+        public DateTime TimeStampUTC
+        {
+            get;
+            init;
+        }
+
+        public string? MerchantSignature
+        {
+            get;
+            set;
+        }
+
+        public string AsString() => $"{TransactionId}|{Name}|{Amount:0.00}|{TimeStampUTC:O}";
+
+    }
+}
diff --git a/QRBee.Core/Data/PaymentRequest.cs b/QRBee.Core/Data/PaymentRequest.cs
new file mode 100644
index 0000000..10a5f40
--- /dev/null
+++ b/QRBee.Core/Data/PaymentRequest.cs
@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace QRBee.Core.Data
+{
+    public record PaymentRequest
+    {
+
+        public ClientToMerchantResponse Request
+        {
+            get;
+            init;
+        }
+
+        public string AsString() => Request.AsString();
+
+    }
+}
diff --git a/QRBee.Core/Data/PaymentResponse.cs b/QRBee.Core/Data/PaymentResponse.cs
new file mode 100644
index 0000000..1f53944
--- /dev/null
+++ b/QRBee.Core/Data/PaymentResponse.cs
@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace QRBee.Core.Data
+{
+    public record PaymentResponse
+    {
+
+        public string ServerTransactionId
+        {
+            get;
+            init;
+        }
+
+        public PaymentRequest PaymentRequest
+        {
+            get;
+            init;
+        }
+
+        public string AsString() => $"{ServerTransactionId}|{PaymentRequest.AsString()}";
+    }
+}
diff --git a/QRBee.Core/QRBee.Core.csproj b/QRBee.Core/QRBee.Core.csproj
new file mode 100644
index 0000000..132c02c
--- /dev/null
+++ b/QRBee.Core/QRBee.Core.csproj
@@ -0,0 +1,9 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>