Some slight progress but still got an error in the end
nginx: [emerg] BIO_new_file("/etc/dehydrated/certs/oip.XXXXXX-it.co.uk/fullchain.pem") failed (SSL: error:02001002:system library:fopen:No such file or directory:fopen('/etc/dehydrated/certs/oip.XXXXXXXX-it.co.uk/fullchain.pem','r')...