Hi @Ashour,
At this time there are no API endpoints to work with Purchase Orders directly, however there are a few different options you have for a workaround, as discussed in this previous thread:
You can look into using the new Inventory Transfers API, to see if this works for your use case.
- New GraphQL APIs for Inventory Transfers Management - Shopify developer changelog
- inventoryTransferCreate - GraphQL Admin
Alternatively, you can create an integration app that works with adjusting inventory manually.
I understand this may not be ideal for you use case, and I will be submitting some feedback to our developers internally on your behalf, additionally you can submit feedback yourself via any page in the Shopify.dev documenation by scrolling to the bottom and selecting Was this page helpful?: No and entering your customized feedback.