The story was initially conceived as a modern retelling of Othello, which is where the names Deb and Ollie/Oleander come from.
Alternatively titled "Crossing the Line".
Lily James is English and plays an American, Tessa Thompson is American who appeared as Valkyrie in several MCU movies with an impeccable English accent.
Lily James, who plays Deb, played Deborah in Baby Driver (2017). In addition, both characters are waitresses.