NCBI EUtils. Get Homolog infromation using Gene ID
From Entrez Programming Utilities Help [Internet]:


  Input: Any Entrez text query (&amp;term); Entrez database (&amp;db);
  &amp;usehistory=y; Existing web environment (&amp;WebEnv) from a prior
  E-utility call


To avoid the error messages, web1, and key1 can be used as terms (these are usually being used to associate with other searches), however this returns no data, probably because the ID you supplied was simply "9", and it remains unclear exactly what you're searching for in the context of other queries.

For example:

esearch.fcgi?db=&lt;database&gt;&amp;term=&lt;query&gt;&amp;usehistory=y

# esearch produces WebEnv value ($web1) and QueryKey value ($key1)

esummary.fcgi?db=&lt;database&gt;&amp;query_key=$key1&amp;WebEnv=$web1


So whilst view-source:eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=homologene&amp;geneid=9&amp;WebEnv=web1&amp;query_key=key1 is a valid query, it's not pointing to anything.