Can not activate

You need to update your version of PHP then.

Please see: https://docs.simplecalendar.io/system-requirements/

The php on the server right? How would I do that? I know how to do it on my computer but how do get godaddy to update their php on the servers?

I am not 100% sure of how you need to go about that. You would need to contact their support to find out your options.