What type of conventions error is present in sentence 22?

(17) The narrator realizes that while Sonny wants to be independent and free he needs his support in order to do so. (18) As a peace offering, the narrator sends a drink of scotch and milk to Sonny at the piano: “He didn’t seem to notice it, but just before they started playing again, he sipped from it and looked toward me and nodded… For me, then, as they began to play again, it glowed and shook above my brother’s head like the very cup of trembling.” (19) The drink is paradoxical in nature, consisting of an alcohol, which is often associated with poison, and milk, which is associated with nurturing. (20) Through this drink, the narrator is telling Sonny that he understands that it is inevitable that Sonny will struggle with his demons, this time the narrator will be there to lend his support. (21) While it is sad that Sonny and his brother must both acknowledge the fact that the suffering will not go away, the ending still has a hopeful tone, because now the narrator realizes what he needs to do and is willing to do it, as implied by the “cup of trembling.” (22) Where before, the narrator shut Sonny out when his addiction became difficult to deal with, now he is ready to welcome his brother in with open arms and support him.

Select one:

There is no error

There needs to be an additional comma after "in"

The comma after "before" is unnecessary

The comma after "with" is unnecessary