PHP form submitting when clicking any buttons

currently setting up a form to create a new order within a payment system and when I click any of the buttons within the form the form submits. Anyone know what the issue could be?
This is the code with the issue:

 <form action="scripts/php/addorder.php" method="POST">
  <script src="scripts/javascript/cookies.js"></script>
  <script src="scripts/javascript/addproduct.js"></script>
  <label>Choose Customer: </label>
  <input type="text" value="" name="name" id="name" required readonly>
  <button onclick ="window.open('customertable.php','popup','width=600,height=600');">Choose</button>
  <br/>
  <div id="products">
      <label>Products: </label>
      <br/>
      ID: <input type="text" value=" " name="chosenproduct0" id="chosenproduct0" required readonly>
      Name: <input type="text" value=" " name="chosenproduct0name" id="chosenproduct0name" required readonly>
      Price: <input type="text" value=" " name="chosenproduct0price" id="chosenproduct0price" required readonly>
      Quantity: <input type="number" value="1" name="chosenproduct0quantity" id="chosenproduct0quantity" required>
      <button onclick ="findproduct('chosenproduct0');">Choose Product</button>
  </div>
  <br/>
  <label>Discount: </label>
  <input type="number" placeholder="0" name="discount" id="discount" step=".01" min="0">
  <label>Total: </label>
  <input type="number" value="0" name="total" id="total" readonly>
  <button onclick="addproduct()">Add Product</button>
  <br/>
  <input type="submit" id="submit" value="Create New Order" class="button"/>
  </form>