This can be done.
Set up two relationships to two Table Occurrences for the same data source table:
To Buy Portal:
ParentTable:: ParentID = PortalTable:: ParentID AND
ParentTable::cPurchaseKey ≠ PortalTable:: Purchased
ParentTable:: ParentID = PortalTable 2:: ParentID AND
ParentTable::cPurchaseKey = PortalTable 2:: Purchased
Set up cPurchaseKey as a calculation that returns the text: "Purchased".
Format PortalTable:: Purchased as a check box field with the single value "Purchased".
Clicking this check box in Portal 1 should drop it out of Portal 1 and make it pop up in Portal 2. (If this doesn't happen instantly, you may need to add a screen refresh or commit record.)
Thanks for the help Phil. I've been trying what you said but I'm struggling.
I've created two new tables one called 'To Buy' the other called 'Purchased' and set up the relationship with the existing master table we use which is called 'Job File'. But all I can do is enter lines into the Purchased portal and when I uncheck them they disappear but don't show up on the other portal. I think I'm a key error by having two separate tables and expecting the data to move from one to the other. Sorry for being so thick.
They should be in the same table. I see no reason from your posts so far to have separate tables.
It's working now. I hadn't tried this before so wasn't quite sure what I was doing hence the dumb questions. Many thanks for your help with this - the prospect of being able to give our team this kind of feature in Filemaker to aid their work is greatly appreciated.