Dear expert,
Please help to give advice on this.
I am trying to restrict custom OVS list based on an SDK field called Billing Mode in Opportunity header.
The OVS refer a BO with structure |LOS|Mat. No.|BillingMode.
In the OVS
I created Root/Inport/BillingMode in data model. Then Bind it with the Parameter BillingMode on the OVSValueSelectorInPort.

In Event AssignEnventHandler, I assign Root/Inport/BillingMode to Root/SearchParameters/BillingMode.

I also add a message box to check the value in Root/Inport/BillingMode and Root/SearchParameters/BillingMode.

Then I use Extensiblity Explorer on Opportunity_TI screen to add OVS for an extension field of node Product.

After activation, when I select the OVS, the message box display empty value for both Root/Inport/BillingMode and Root/SearchParameters/BillingMode. The list in OVS is also not filtered correctly.

I have look through every post about OVS but I found nothing that can help. Please help to give advice.