I receive the following error whenever I start up my server;
" MissingFieldException: Field 'ProtoBuf.VendingMachine/SellOrder.instanceData' not found. "

I have tried to remove all plugins with not avail, I've used the last Oxide version before the Rust update and it worked fine.
Any ideas?

Make sure to update Rust before Oxide. The error means you're mixing Rust versions. The latest Oxide update was also for a Rust update.