Unable to access Membership in Admin role

Hello. I have just uploaded the Membership plugin to my site, and there is no menu for it in the admin sidebar.
I noticed in the admin bar (top right) ir says Membership: Disabled. I clicked this, and then on the Enable Membership option.

However I am then taken to a plain gray screen which shows this.

I am the owner/admin of the site and confused as to why this is happening.

Please help asap.

Many thanks, Andrew.