function.php

<?php 
function limit_upload_file_size( $file ) {
	
  // Check if upload field is ACF file
    // Get max upload file size
    // Set max upload file size to max upload file size of field
  // else
    // Max upload file size === 300kb
  // endif
	return $file;
	
}
add_filter ( 'wp_handle_upload_prefilter', 'limit_upload_file_size', 10, 1 );