I’ve been working with that API recently after a long break since 8.1 or 8.2, I saw that REST calls to one particular method of NACEndSystemWebService began to fail. The mainstream approach is to move to NBI (GraphQL, JSON over REST, I don’t know how to actually define that mix of terms) AFAIU.
What is cool in that, you either send a query or a mutation and within you specify what API component you refer to, and what exact data you wish to pull/modify, no longer fixed bulky request/response schemes.
If you need any advice on switching to this approach, let us know.
Hope that helps,