<?php 
  $total = 0;
  while(the_repeater_field(\'repeater\' )): 
      the_sub_field(\'space_avail\' );
      $total += intval( get_sub_field(\'space_avail\' ) );
  endwhile; 
  echo $total;
?>

Try this:

$total = 0;
while(have_rows(\'repeater\')) : the_row();
    $space_avail = (int)get_sub_field(\'space_avail\');
    $total += $space_avail;
endwhile;

echo $total;

删除：

the_sub_field(\'space_avail\' );

acf documentation repeater fields

    // loop through the rows of data
while ( have_rows(\'repeater_field_name\') ) : the_row();

    // display a sub field value
    the_sub_field(\'sub_field_name\');

<?php 
  $total = 0;
  while(the_repeater_field(\'repeater\' )):       
      $total += intval( get_sub_field(\'space_avail\' ) );
  endwhile; 
  echo $total;
?>

<?php 
  $total = 0;
  while(the_repeater_field(\'repeater\' )): 
      the_sub_field(\'space_avail\' );
      $total += intval( get_sub_field(\'space_avail\' ) );
  endwhile; 
  echo $total;
?>

Try this:

$total = 0;
while(have_rows(\'repeater\')) : the_row();
    $space_avail = (int)get_sub_field(\'space_avail\');
    $total += $space_avail;
endwhile;

echo $total;

删除：

the_sub_field(\'space_avail\' );

acf documentation repeater fields

    // loop through the rows of data
while ( have_rows(\'repeater_field_name\') ) : the_row();

    // display a sub field value
    the_sub_field(\'sub_field_name\');

<?php 
  $total = 0;
  while(the_repeater_field(\'repeater\' )):       
      $total += intval( get_sub_field(\'space_avail\' ) );
  endwhile; 
  echo $total;
?>