This section is for your developer.
Login to your MailExpress account, go to Settings -> Integration / APIs
https://app.mailexpress.com/settings/api
You will find the API Token, Instructions, and Samples for:
- Add Contact
- Unsubscribe Contact
- Delete Contact
- Check Subscription Status in List
- Update Custom Fields in List
- Send Email to Subscriber
- Get Subscription Data
- Change Contact's Email Address with List ID
