Unable To Edit Sandbox Subscription URL

When trying to open a subscription, I get the following error:

{
  "message": "Your subscription url is a websocket url, so your server must support graphql-ws or subscriptions-transport-ws protocol. If your server supports HTTP multipart subscriptions, change your subscription url to HTTP."
}

My server does support multipart subscriptions. But, when I go to the configuration to try and edit the subscription URL, it is not editable.

Screenshot 2024-05-07 at 12.34.08 PM

Is there a setting somewhere that I need to change to enable editing? I’m using the ApolloServerPluginLandingPageLocalDefault plugin. Thanks!