Fixed: Error adding import list exclusions from discover

Fixes #6739

frontend/src/Store/Actions/discoverMovieActions.js

@@ -600,6 +600,7 @@ export const actionHandlers = handleThunks({
     const promise = createAjaxRequest({
       url: '/exclusions/bulk',
       method: 'POST',
+      contentType: 'application/json',
       data: JSON.stringify(exclusions)
     }).request;