2719199 - Unable to retrieve the external data due to: (HTTP 503) 4_Cannot open tunnel with id account:/// in SAP Analytics Cloud

The following error appears when trying to import or export data into SAP Analytics Cloud (SAC):

• sap.fpa.services.resource.dm

  Unable to retrieve the external data due to: (HTTP 503) 4_Cannot open tunnel with id account:///

  sap.fpa.services.resource.dm

  Unable to retrieve the external data due to: 4_{"packageId":"sap.fpa.services.resource.dm","objectName":"message_dm","messageId":"SERVICE_NOT_RETRIEVED","args":["(HTTP 503)  4_Cannot open tunnel with id account:///"],"message":"Unable to retrieve the external data due to: (HTTP 503) 4_Cannot open tunnel with id account:///","stack":"Exception@/sap/fpa/services/core/system/Exception.xsjslib:120\nExceptionServiceProxy @/sap/fpa/services/dm/ServiceProxy.xsjslib:595\nServiceProxy.prototype._reconstructExecuteServiceResult @/sap/fpa/services/dm/ServiceProxy.xsjslib:1112\nServiceProxy.prototype._executeServiceAndReconstructResult @/sap/fpa/services/dm/ServiceProxy.xsjslib:941\nServiceProxy.prototype._executeServiceInternal@/sap/fpa/services/dm/ServiceProxy.xsjslib:1001\nServiceProxy.prototype.executeService @/sap/fpa/services/dm/ServiceProxy.xsjslib:822\nCloudConnector.prototype._addAuthorizationHeaderAndExecute@/sap/fpa/services/dm/CloudConnector.xsjslib:248\nCloudConnector.prototype.execute @/sap/fpa/services/dm/CloudConnector.xsjslib:213\nBPC10Service.prototype.getCubeSetList@/sap/fpa/services/dm/bpc/BPC10Service.xsjslib:71\nDataIntegration.prototype.getCubeSetList @/sap/fpa/services/dm/bpc/DataIntegration.xsjslib:63\nRestDataIntegration.prototype.doPost@/sap/fpa/services/dm/RestDataIntegration.xsjslib:201\nhandleRequest @/sap/fpa/services/GetResponse.xsjs:287\n@/sap/fpa/services/GetResponse.xsjs:336\n","bUIMessage":false,"bWarning":false,"bpcRequestStatusCode":503}

• SAP Analytics Cloud 2018.19.3

SAP Cloud for Planning, sc4p, c4p, cforp, cloudforplanning, EPM-ODS, Cloud for Analytics, Cloud4Analytics, CloudforAnalytics, Cloud 4 Planning, BOC, SAPBusinessObjectsCloud, BusinessObjectsCloud, BOBJcloud, BOCloud., SAC, SAP AC, Cloud-Analytics, CloudAnalytics, SAPCloudAnalytics , KBA , LOD-ANA , SAP Analytics Cloud (SAC) , LOD-ANA-BI , Business Intelligence Functionality, Analytic Models , LOD-ANA-PL , Planning , LOD-ANA-BR , SAC Boardroom , LOD-ANA-PR , SAC Predictive , Problem