Bizhub 363 will not print 2 single letter size copies to one double side anymore, keeps saying matching paper size is not available. What do I need to do

Check the paper size setting for both the computer and the copier.

Sounds like you have a mismatch in the paper you are trying to print on and the paper that is loaded in the printer. HP printers look to feed paper from tray 1 anytime the computer settings don't match the paper loaded in tray 2. Tray 1 is the multi purpose tray and prety much any size paper can be loaded in tray 1. Double check your document settings and double check the paper size loaded in the paper tray 2 and make sure they match. Also try printing a different document to see if the error persists. If it does this on everything you try to print you should also double check teh rear guide in the paper tray. There is a rear guide in paper tray 2. If it slides back too far it will make the printer think that paper longer than 8 1/2 x 11 is loaded. Push the paper all the way forward in the tray and push the rear guide until it is snug with the tail end of the paper stack.

sometimes especially when printing a pdf there is a box on the first print screen that pos up that says print actual size deselect that and then it will default and print on the paper that is available

A4 is n earupean size .change to 8 1/2 by 11 in both the copier and you printer setting..

Change the marketing area from EU to US in Service mode.

Does your machine have double siding capabilities?
If so on the control panel under original / copy. select 1:2, this will give you a double sided copy from a pair of single originals even off the glass.

There are two possible culprits for this problem.

1. The wrong driver is being used for your printer.

2. The paper thinks it is printing to different sized paper than it actually is.

To solve the first case:
Verify that the correct driver is being used. Go to the Control Panel (Start, Settings, Control Panel) and open up the Printers and Faxes component by double-clicking on it.
Right-click on your printer and go to Properties.
A new window will pop-up. Go to the Advanced tab and verify next to where it says 'Driver' that it lists your model of printer.

To solve the second case:
Exactly as you did above, under the Advanced tab, click on the 'Printing Defaults' button.
Then click on the Paper/Quality tab on the new window.
Under the Paper/Quality tab click on the 'Advanced' button.
A new window will pop-up. Where it says Paper/output, expand it (click the plus) to list Paper size. Change Paper size to match the size of the paper you are printing (Letter is the default 8.5" x 11").

go in youre ip address, log in as admin, chooce print tab and there is a print tab, there is a default options, and choose double printing off

What that is saying is that somewhere, most likely in a print job, either the paper tray settings or the settings on the driver are incorrect.
What you need to do is look at the machine paper tray settings and see if they all say the proper size and paper type, and that they match the driver settings.
An example. See that the letter tray settings are 8 1/2 x11 plain paper on the machine and driver. Be for example that the driver doesnt say plain paper and the machine bond, or recycled, or heavyweight. They MUST match or you will receive that message.
The paper SIZE snd TYPE must match.