Fatal Error Message After image upload

Whenever I upload an image for the favicon, I get two messages. At the top of the screen it says that the favicon was successfully installed. But just below that it says this:

Fatal error: Call to undefined method DateTime::getTimestamp() in /home/content/52/11131252/html/wp-content/plugins/genie-wp-favicon/GwpfSetupModel.php on line 25

I tried deactivating the plugin, but the image I chose is still appearing in the window tab. I tried reinstalling it and using a different image, but it does the same thing and won’t even recognize the new image.

What should I do?

https://www.ads-software.com/extend/plugins/genie-wp-favicon/