In many US states, even a verbal contract is legally binding. Obviously this depends on many factors, the terms have to be reasonable and it has to be clearly communicated (and it’s generally harder to prove a verbal contract in court). Text and email communications are the same way.

In your example, it likely wouldn’t be considered a valid contract though. The terms have to be reasonable for both parties and there has to be a clear understanding that it is an agreement. Getting “ok” back is presumably sarcastic or not genuine.