Hello,
Adding to the other replies... Few things to check:
Location Card - I see the setup shows Require Receive checked.

Note that my Location will allow me to create Warehouse Receipt and Warehouse Shipment and a Bin Code is mandatory. Now lets create a Purchase Order.

The Qty to Receive is blank, since Require Receive is set to Orange Location. I click Actions/Warehouse/Create Whse. Receipt

Under Warehouse Setup, make sure your Number Series is setup. The Require X come from the Location so no need to set this.

Check my settings with yours and test again.
Hope this helps.
Thanks.
Steve