Display an error message in php form

Ok, I want to tell this form, if it has some content the text type input and one of the radios in this case the one that has the final value (both at the same time), then send a message, can not choose the input text and the radio with the final value at the same time, but only that radio in specs.

I hope it gets better understood ... just that it does not come out is isset or with the if.

I do not put the button because it has not let me put it here, but it is a single send button ...

Sorry but I am a beginner in php and javascript ...

formulario.php

<form action="index.php" class="form-group" method="post" target="_blank">

    <div>
        <input type="text" name="inning" placeholder="inning" requiredd="requiredd" class="form-control">
    </div>


    <div class="custom-control custom-radio  col-12">
        <input type="radio" id="customRadioInline1" name="customRadioInline1" value="upu" class="custom-control-input" required="required">
        <label class="custom-control-label" for="customRadioInline1">
            <img src="img/up.jpg" width="20" alt="">
        </label>
    </div>
    <div class="custom-control custom-radio col-12">
        <input type="radio" id="customRadioInline2" name="customRadioInline1" value="down" class="custom-control-input col-12" required="required">
        <label class="custom-control-label" for="customRadioInline2">
            <img src="img/down.jpg" width="20" alt="">
        </label>
    </div>
    <div class="custom-control custom-radio col-12">
        <input type="radio" id="customRadioInline3" name="customRadioInline1" value="final" class="custom-control-input col-12" required="required">
        <label class="custom-control-label" for="customRadioInline3">FINAL</label>

Sorry, I do not know how to put the code very well, it's my first post ...