Hello Tommy,
This happens because SoapUI by-default trust everything so you don't need to explicitly upload HCI server root certificate into SoapUI trust-store.
Reason we upload root certificate of HCI to ERP because unlike SoapUI which is a testing tool , ERP system can not connect to any external system until it's trusted by ERP. For ERP to trust HCI we need to upload valid root certificate of HCI server into ERP trust store.
Regards
sharad