Is it possible to use custom workflow for approvals of pruchase requests? I think the answer is no, we're limited to standard approvals. But please correct me if I'm wrong !

I haven't worked with purchase request but I don't see why you can't use custom approvals. Unless you cannot deploy workflow/script to this record.

It cannot be select as a Transaction sub type for triggering in the workflow. Also when you go to setup accounting, it isnt there to select for Approval Routing

That seems like a blocker then...

take a look at suite answer: 11109. In short see screenshot.

It seems that you haven't enabled Purchase Reqs yet, @Mika Hakkinen

@Mika Hakkinen I currently use a custom workflow for purchase requests. Once you enable purchase requests the Approval Status and Next Approver fields become available for workflow. Also the Purchases to Approve suite let

Bizarre, definitely enable purchase requests, I've been testing with it! @al1, what sub type do you use for your custom approval workflow? As I mentioned earlier, the purchase request sub type isnt on my list!

Use purchase order