<div class="col-md-12">
<label>Enter Amount:</label>
<input type="text"  class="form-control" id="inputValue"   value="">
</div>

<div class="col-md-12">
     <label>Total Amount Paid:</label>
         <input type="text"  class="form-control"
         readonly="readonly"id="totAmountPaid" value="">
</div>

<div class="col-md-12 ">
      </br><button class="btn btn-primary col-md-6" type="button"
               onclick="myFunction()" >btn</button>
</div>

script
function myFunction(){
 var paidAmount = parseFloat(document.getElementById("inputValue").value);
document.getElementById("totAmountPaid").value =  paidAmount.toFixed(2);
}

<div class="col-md-12">
     <label>Total Amount Paid:</label>
         <input type="text"  class="form-control"
         readonly="readonly"id="totAmountPaid" value="">
</div>

<div class="col-md-12 ">
      </br><button class="btn btn-primary col-md-6" type="button"
               onclick="myFunction()" >btn</button>
</div>

function myFunction(){
 var paidAmount = parseFloat(document.getEle`enter code here`mentById("inputValue").v`enter code here`alue);
document.getElementById("totAmountPaid").value =  paidAmount.toFixed(2);
}