q parameter not working with ADF describe service connection

I have created service connection using 'Define by specification' and ADF describe option.

/fscmRestApi/resources/11.13.18.05/itemStructures/describe with get all end point

Used this service connection in action chain call REST as endpoint with the q parameter as give below

"ItemNumber=" + $page.variables.ItemNumber

But the end result not filtering data for specific item and instead giving result for all items.

Please let me know what cloud be the issue

Thanks

Santhosh