Setting a property and using it to filter data

I am trying to use a drop-down list to select and id and use this to filter a grid, but it does not work.
Here is where I create the property on the page load:

Then, when the user changes the value, I need to set my selectedTeacher property to the selected id (this is the change event in my drop-down list control):

The drop-down is populated by a stored procedure, which is working fine:

But when I change the value, I get this error message:

I am currently re-creating an Radzen angular application where this is working fine, but no such luck with a Radzen Blazor webassembly application. This is probably me not understanding types properly.
Any help would be appreciated.

Unlike Angular DropDown Change event in Blazor will provide directly the value not the entire object, check the exception for reference.

Thanks enchev, it now works correctly.