I have a 404 error logfile (from another plugin) which shows all the 404 errors on my website. I noticed that it is getting a lot of hits for this:
I also noticed that the button icon is missing from the "Add Content Block" button in my Visual Editor. The button only has the text and no icon.
And don't worry, I already know the reason for this error! :) It's because I have renamed my wp-content folder to something else, by using the define('WP_CONTENT_URL') setting in my config.php file.
The icon is missing because you have hard-coded the name of the wp-folder in the post-widget.php file of your plugin - on line 213 and 217. Therefore the button can't load, and gives a 404 error every time.
Can you kindly fix this please, by removing the hard-coding of this folder path and using whatever WordPress variable exists for the wp-content folder? (I don't know what the correct variable is, but I know that it is possible to take the correct path based on what is set by the WP_CONTENT_URL in my config.php tile).