Ajax query result success call multiple times – Jquery ajax

I have an ajax call where success function is called twice. I tried to analyze but not getting why it is getting called twice.

I am using a for loop to call ajax functionality and inside that I am calling second ajax inside success function based on a condition (f==i+1). If the condition matches then it will call second ajax functionality, but what is happening is that, after the loop is over, inside the success of first ajax call is calling alert("Check call"); twice. It should call only once if i=1 in the loop.
What is happening in first loop is the condition doesn’t go to success and when the loop is over then it goes to success of first ajax as many time as loop happen and f become 2 and i+1 become 2 so it will check condition two times.

Any help would be appreciated.

    $(document).on("click", "#Rsub1", function (e) {
        if ($("#Rvno").val() == "" || $("#Rvno").val() == null) {
            alert("Please enter Vendor no");
        } else {
            for (var f = 0; f <= i; f++) {
                (function (index) {
                    $.ajax({
                        type: "POST",
                        url: "../Home/RaisePReq",
                        data: formData,
                        dataType: 'json',
                        contentType: false,
                        processData: false,
                        cache: false,
                        success: function (r) {
                            if (f == i + 1) {
                                alert("Check call");
                                var fieldvals
                                $.ajax({
                                    type: "POST",
                                    url: "../Home/gridtbl",
                                    data: JSON.stringify(fieldvals),
                                    contentType: "application/json; charset=utf-8",
                                    datatype: "json",
                                    success: function (r) {
                                        $('#grdtbl').html(r);
                                        //jQuery.noConflict();
                                        $('#ipcelltbl').DataTable({
                                            dom: 'Bfrtip',
                                            buttons: [
                                                'copy', 'csv', 'excel', 'pdf', 'print'
                                            ]
                                        });
                                    },
                                    failure: function () {
                                        alert("Error");
                                    }
                                });
                            }
                        },
                        failure: function () {
                            alert("Error");
                        }
                    });
                })(f);
            }
        }
    });