Hi @sadsergius, based on your description it looks like your webhook only has a single item, but your Nextcloud node actually gets three items. So you probably ran into this problem here.
Instead of using an expression like /{{ $node["Webhook"].json["body"]["name"] }}/{{Object.keys($node["Webhook"].json["body"])[0]}}/{{$binary.data.fileName}}, could you try the one below?
/{{ $("Webhook").first().json["body"]["name"] }}/{{Object.keys($("Webhook").first().json["body"])[0]}}/{{$binary.data.fileName}}
Using .first() should always point to the first (and only) item of your Webhook node, hopefully avoiding this problem.