Category directs to Invalid URL

I have just created my first “category” for my blog, however when i went to test it out i found that the link that wordpress had generated was invalid.

My website is https://garden-bird-feeders.co.uk/ , and if you click on the ‘Summer 2010 Range’ category link you will be directed to: https://garden-bird-feeders.co.ukcategory/summer-2010-range

Can anyone help me on how to fix this? Thanks