Zend certified PHP/Magento developer

oAuth1 initiation – 404

I’m trying to get oauth access token for a third party application, following documentation here.
However, I always end up with a 404 error. I tried with different clients (python and postman), with different signature methods (HMAC and PLAINTEXT). I also tried to put the oauth_callback as a request param (against offical doc, but I saw that in another tutorial) but it didn’t help either. I’m attaching a screenshot displaying the python script used and the output showing the correctly constructed Authorization header (I’m not sure if I should put the /index.php in the BASE_URL so I tried both). Also, I (obviously) anonymized the key and secret after execution.

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I’ve been struggling with this for a few days now, any help will be really appreciated.

Thank you.