commit is a api parameter, which is known as Up-front payments in trhe control panel, see api docs: https://api.99stack.com/docs/#operation/server-create.
What it means is basically that in order to deploy a smtp enabled server, you need to have it for at least 3 days (72 hours). I suppose it's a precaution to prevent spam, or to make it harder and way more expensive for people intending to abuse the service.
This is not really an issue if you're sending legit emails, as your dedicated ip address will not get blacklisted. In fact, if you select 3 months
commit or Up-front payment for at least 3 months, you can save 70% on the server price.