multilingual website issue with slug

Hello

I need some support please. I am new to WP. We have created a website in Spanish https://agogopizza.com/es/. Under languages we have created the new language, local en_GB, code en; and we have translated the Spanish page into English. We have added to the menu in the Spanish mage the option of the language showing only the flag and not displaying the language being used.

The problem is that when you then click on the flag for English it directs you to https://agogopizza.com/en/, which is actually correct as we want the English version to have this URL, where we replace the es by en. When i open in WP the English page to edit I see it has a URL slug. If I change it to en, i get an error when opening the url https://agogopizza.com/en/ “The page can’t be found.”. If I change the slug to something else like https://agogopizza.com/en-en and i type the URL in the browser it displays but the problem is that the menu is targeting the https://agogopizza.com/en/ page.

How can I fix this?

We have the Polylang plugin installed version 2.6.7
WordPress version 5.3.2

Thanks in advance for your help.
Cheers

Camilla