acf-slider.php

<?php if ( get_field( 'slides' ) ) : // repeater field ?>
    
    <ul class="slider">
        <?php while ( the_repeater_field( 'slides' ) ) :
            $image = get_sub_field( 'slide' ); // sub-field image ID
            $slide = wp_get_attachment_image_src( $image, 'slides' );
            $alt = get_post_meta( $image, '_wp_attachment_image_alt', true );
            ?>
            <li><img src="<?php echo $slide[0]; ?>" alt="<?php echo $alt; ?>"></li>
        <?php endwhile; ?>
    </ul>

<?php endif; ?>