Create flex fields for an existing sales order

Summary:

Hello everyone, I have the following problem that requires your support:

• I have a sales order created in the ERP
• A context has already been created with the flexfield associated at the header level. (It is displayed on the screen)
• I need to use a Rest service that allows updating the value of the flexfield at the header level. If you don't have one, you must create one.

So far I have tried the following documentation using example 4 which is the closest to what I require, but I get error 404.

https://docs.oracle.com/en/cloud/saas/supply-chain-and-manufacturing/24c/fasrp/op-salesordersfororderhub-orderkey-patch.html