Tumblr Button Error

Clicking the Tumblr button on any post on any of the sites I’m using the SSBA plugin on currently returns a ‘not found’ error:

The URL called is: https://www.tumblr.com/widgets/share/tool?shareSource=legacy&canonicalUrl=&url= [plus URL]

And the error message is:

There’s nothing here.
Whatever you were looking for doesn’t currently exist at this address. Unless you were looking for this error page, in which case: Congrats! You totally found it.

Does the plugin need to be updated to take a new Tumblr API into account or something?

https://wordpress.org/plugins/simple-share-buttons-adder/