3333785 - "Could not enable Identity Authentication" error occurred when enabling IAS in BTP Work Zone, standard edition

• You want to enable BTP Work Zone, standard or advanced edition to use SAP Cloud Identity Services - Identity Authentication as unique authentication method.
• After clicking the "Enable" button, you face the following error:
  Error Could not enable Identity Authentication. Please open a ticket to the relevant component.
  
  

• If you check the http network trace in browser developer tool (F12), there's a request similar as below:
  https://<hostname>.launchpad.cfapps.<region>.hana.ondemand.com/tenant-configuration/item?key=movedFromSaasProvisioning&_=xxxxx
  
  Within the request, check the Content tab, it contains the following message:
  {
      "key": "movedFromSaasProvisioning",
       "value": {
           "state": "SUBSCRIBE_FAILED",
           "info": "update subscription failed. Error: subscribe failed in create IAS subscription. Error: CorrelationId: xxx, Details: Error handling subscription in IAS: Subscribe: IasSubscriptionDto(id=, zoneId=xxx, iasServiceInstanceId=xxx, redirectDomain=, information=null) failed. Reason: IAS Post request error! Reason: 422 : \"To subscribe this application link an Identity Authentication tenant to the subaccount with the \"Establish Trust\" option. For more information: https://help.sap.com/viewer/65de2977205c403bbc107264b8eccf4b/Cloud/en-US/161f8f0cfac64c4fa2d973bc5f08a894.html\" Status code: 422 Body: To subscribe this application link an Identity Authentication tenant to the subaccount with the \"Establish Trust\" option. For more information: https://help.sap.com/viewer/65de2977205c403bbc107264b8eccf4b/Cloud/en-US/161f8f0cfac64c4fa2d973bc5f08a894.html .",
           "iasTenantUri": "https://<tenant name>.authentication.<region>.hana.ondemand.com"
       }
  }

SAP Build Work Zone, standard edition

oidc1.0, xsuaa, accounts.sap.com,  accounts.cloud.sap, ias, subscribe failed, Could not enable Identity Authentication, booster, work zone, standard edition, advanced edition, subaccount configuration, api call. , KBA , EP-WZ-SM , Site Directory, Site Settings, Site Service, IAS Integration , BC-CP-CF-SEC-IAM , UAA, Authentication, Authorization, Trust Mgmnt , Problem