Error when generating images

/wp-content/plugins/auto-post-thumbnail/admin/views/tab-generate.php on line 203
"> 

Warning: Undefined array key "image_size" in /wp-content/plugins/auto-post-thumbnail/admin/views/tab-generate.php on line 209

Screenshot https://i.imgur.com/TbfbChN.png

All done as usual, I can not understand why the plugin does not want to generate images. Please tell me what to do.