Problems with Ariba Network Purchase Orders Supplier API

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I'm experiencing several issues with the Ariba Network Purchase Orders Supplier API:

1. Paging Issues: Paging doesn't work as expected. When retrieving items without filters, starting from page 2, the results are inconsistently sorted. I often see duplicates from page 1, which results in incomplete and redundant data.

2. Filtering by Document Number: Filtering by documentNumber for older orders is cumbersome. If an order is older than 31 days, I need to specify both a start and end date to find it, but this date range is often unknown.

3. No POST Endpoints: There are no POST endpoints available to, for example, confirm an order or add data to it. This can only be done via the Ariba frontend, which limits automation possibilities.

4. Limited Sorting Options: The order_by options are very basic. I can only sort by supplierId or buyerId, which are identical across our records. There's no way to sort by date or documentNumber, which would be far more useful.