Our customers are using different CRM (Customer relationship management) and ERP (Enterprise Resource Planning) systems. The most uses systems are:
SAP ECC
SAP 4 Hana
Microsoft Dynamic
IBM AS 400.
Some customers have their own built system.
For communication with these systems are used CSV/XML files transferred via SFTP or S3 storage or API which these systems provide which are usually REST or SOAP call.
It is good if the integration engineer has user or technical experience with some of these systems.