This error can occur for various reasons, but the most common one is when the folder permissions are incorrect.

You see, every file and folder on your website has a set of permissions that determine who can access them and what actions can be performed on them. These permissions are controlled by your web server.

Now, if the permissions for a particular folder are set incorrectly, it can prevent you from writing or adding new files to that folder. Essentially, your web server loses the ability to create or modify files in that specific location.

When you attempt to upload images or any other files through the WordPress admin area, you may encounter one of the following error messages:

1. “WordPress failed to write to disk”
2. “WordPress has failed to upload due to an error: failed to write file to disk”
3. “Unable to create directory wp-content/uploads/2016/03. Is its parent directory writable by the server?”

These messages indicate that the server is unable to write or create files in the designated folder.

In simpler terms, it’s like trying to save a document to a folder on your computer, but the folder is locked and you don’t have permission to add or modify files within it.

First try to narrow down the problem’s source and then for further queries post the same . will reach out if i have a solution