SOAP API
Legacy SOAP-based API for Marketing Cloud operations, including email sends, subscriber management, and data extension operations.
Documentation
Documentation
https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/web_service_guide.html
APIReference
https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/soap_web_service_objects.html
GettingStarted
https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/getting_started_developers_and_the_exacttarget_api.html
BestPractices
https://developer.salesforce.com/docs/marketing/marketing-cloud/guide/working_with_soap_web_service_api.html