Hello @doufenglai,
My apologies, this change was included in another plugin that share with this part of the core, please, follow the steps below:
1. Open the “/wp-content/plugins/sell-downloads/sell-downloads.php” file with the text editor of your choice.
2. Go to the piece of code:
update_option('sd_old_download_link', @intval(stripcslashes($_POST['sd_old_download_link'])));
and edit it as follows:
update_option('sd_old_download_link', @floatval(stripcslashes($_POST['sd_old_download_link'])));
and that’s all. Now enter the number 0.21 as attribute’s value in the store’s settings.
Best regards.