https://help.sap.com/docs/TASK_CENTER/08cbda59b4954e93abb2ec85f1db399d/d26b525d88574afdae98428d65f26fd9.html?locale=en-US
A hint like for other Task Provider systems that the Token Service URL is data center dependend would be helpful. Cost some time to figure out that api.ariba.com isn't a generic host.
Maybe a reference to SAP Note 3178875 - How to generate the OAuth Access Token for an API:
You can find the value of OAuth Server URL Prefix for your region on the SAP Ariba Developer Portal on the Discovery page for any API in the Environment Details table. Please login to the developer.ariba.com and choose the region where your realm resides.
https://help.sap.com/docs/TASK_CENTER/08cbda59b4954e93abb2ec85f1db399d/d26b525d88574afdae98428d65f26fd9.html?locale=en-US
A hint like for other Task Provider systems that the Token Service URL is data center dependend would be helpful. Cost some time to figure out that api.ariba.com isn't a generic host.
Maybe a reference to SAP Note 3178875 - How to generate the OAuth Access Token for an API: