I don't have a cURL request, but here's the createPlan that we are sending, and that doesn't seem to appear in your API reference anymore:

const createPlan: TrieveKnowledgeBaseCreate = {
                type: 'create',
                chunkPlans: [
                    {
                        fileIds: [fileResponse.id],
                        websites: [],
                        targetSplitsPerChunk: 1,
                        splitDelimiters: ['~'],
                    },
                ],
            };