Screen states "Wrong size paper." It's same paper always used. ??

Before printing you need to select the size and orientation and it's a good idea to look at the preview before printing. That saves a lot of paper.

What the problem sounds like is that the machine and print driver are set to diifferent paper types.
One says plain paper and the other bond paper.
Or something like that, the machine says bond and the printer plain paper.
Chech the size setting and paper orinentation.
Most of the time the paper type is wrong. Also check paper color etc etc. Something between the machine and driver is mismtached
Check this : https://printerguidelines.com/

Check the dial or slider on the side of the cassette tray for size indicator. This will cause jamming and the improper size message. Make sure the indicator matches the size of paper in the tray.

Verify your settings under the Paper Menu are correct as far as size and type. All trays with same size and type settings are automatically linked as per the User Guide.

You just stated the problem yourself!!!!!!!!!!!!!!!!!!!!!

Are you using Letter or Legal?? then the tray need to be set to that particular size.

If using Legal set to Legal, otherwise the machine will automatically know you are using the wrong size.

Your printer is set to default to the Main Paper Feeder, which is probably set for letter size paper. You must tell it to feed cards. On your Windows Desktop, left click mouse on START. left click on CONTROL PANEL, and left click on the PRINTERS icon. On the PRINTERS screen, RIGHT CLICK on your Dell printer icon. On the drop down menu, left click on PRINTING PREFERENCES. On the PRINTING PREFERENCES window, left click on the PAPER/QUALITY tab. Under TRAY SELECTION, choose the PAPER SOURCE where you want your business cards to feed from. Left click on APPLY button. Next, left click on the ADVANCED button. On the ADVANCED OPTIONS window, use the drop-down box next to PAPER SIZE to choose the paper size you want to feed. Press OK button. The PRINTING PREFERENCES window will now reappear. Left click APPLY, then OK buttons. After you have printed your cards, be sure to restore the printer defaults back to their original state, or the printer may jam because it must be programmed for the paper size being used. If you reload letter paper without resetting the paper size, the printer will think there is still card sized paper in the tray, and it will issue a jam or error code until the paper size is set properly.

First make sure that the machine is reading/ seeing the paper size of the paper that is in the tray ( select tray 1 from the touch screen and see what the paper size reads). If the machine sees a different size then that in the tray, use the 'user tools' and change the paper for that tray. Also, go into your printer settings on/in your computer and make sure that the proper paper size is selected ( the size that is in the tray you want to print from). If the orientation of the paper size is different from the tray -- will not print and give you the error.

check document paper size, sounds like you have changed paper size on print driver but what of the document you are trying to print? what size is that? is it still letter or have you set page size also to 4 x 6

Try this first..... Some faxes can be configured for different paper sizes for timing of the preinting process. This would be either tabs on the back of the paper drawer of a soft setting found in the owners manual.