Using REST API to opt in emails

We are trying to get the REST API to opt in email addresses when the user checks an opt in checkbox on our form. All answers that i have found on here are about 2 years old and say that they are working on it. Anyone have an idea of how this is coming along?!/Contact/createContactUsingPOST!/Contact/updatePropertiesOnContactUsingPATCH_1

You may opt-in or mark a Contact as Marketable by including the following field in the request JSON with an opt-in reason. (This field is also shown in the complete request body sample.) The reason you provide here will help with compliance. Example reasons: "Customer opted-in through webform", "Contact gave explicit permission."

Thank you Tom I think we have the creation sorted. Just need to work on updating if they submit the form a second time using that second link.