When trying to perform any PUT or POST command on the REST API (v3) over a http connection, the user receives a "501 Method Not Implemented" error.
The error occurs for instance on updating products (one product or in bulk) using the Python official library, cURL or the PHP library.
GET commands work as intended. Please note that the issue occurs even though the user credentials refer to an admin account, which has read/write access in the WooCommerce API.

The exact error message is:
PUT to /wc-api/v3/products/156 not supported.
(while 156 refers to a valid product id)