Incrementing IDs with Wordpress ACF loop

Question

I have loop in WordPress and I am trying to get increment values for IDs, my code looks like this:

<?php if(get_field('repeater_field_name')): $i = 0; ?>
    <ul>
    <?php while(has_sub_field('repeater_field_name')): $i++; ?>
        
        <li class="HR-<?php echo $i; ?>">
            sub_field_1 = <?php the_sub_field('sub_field_1'); ?>, sub_field_2 = <?php the_sub_field('sub_field_2'); ?>, etc
        </li>
    <?php endwhile; ?>
    </ul>
<?php endif; ?>

This code gives me an output like this:

<li class="HR-1"></li>

What am trying to achieve is output like this:

<li class="HR-01"></li>

An know that I can add 0 but then the output will be like this:

<li class="HR-010"></li>

IDs from 0-9 needs to be like this:

<li class="HR-01"></li>
<li class="HR-02"></li>

IDs from 10 needs to be like this:

<li class="HR-10"></li>
<li class="HR-11"></li>

Can anybody try to help me with this?