Translation:The total that he demanded was ten euros.
This looks very strange after being taught for a few months now that usually an 'infinitive' would follow "postulis". Did I miss a lesson somewhere?
No, you missed the fairly common linguistic trick of using a phrase as an adjective. The phrase kiun li postulis describes "sumo" and is treated in relation to the rest of the sentence as if there is no verb in it .
I'm sure that one of the language wonks can give you a more definitive explanation, I'm just remembering High School English classes here.
No, it's a fairly good explanation.
"ke li postulis" is a subclause and refers to "sumo". The verb "estis" that comes next is the main verb of the sentence, with subject "sumo".
The subject of "postulis" is "li".
Hope that clarifies.