paper size mismatch

[peppermint]

I have used this printer for a long time and given me no problems.  Suddenly I get the paper size mismatch message.

[sandytechy20]

@peppermint

Welcome to the HP support community.

I understand that you are getting paper mismatch errors while printing, I am glad to assist you.

What size of paper are you trying to print on?

Which application are you using to print?

Did you try a different application to print?

Meanwhile:- 

Check the paper size and source settings

Check the paper size and source settings for your print job in macOS.

1. In the program you are trying to print from, click File, and then click Print.

2. Make sure your printer is selected, and then click Show Details.

3. Select Paper Type/Quality or Media & Quality.

4. Click Feed from or Source, and then confirm the correct paper tray is selected.

5. Check the paper size settings.

   • If a Paper Size option displays, click it.

   • If a Paper Size option does not display, click Cancel, click File again, and then select Page Setup.

6. Make sure the paper size matches the type of paper loaded into the printer.

   NOTE: 

   If the exact paper size is missing from the list, select the size closest to the paper loaded into the tray.

7. Click OK.

Reset the printer

Reset the printer to recover from printer errors or failures.

1. If your printer has a rechargeable battery, remove it.

2. With the printer turned on, disconnect the power cord from the printer.

3. Unplug the power cord from the power source.

4. Wait 60 seconds.

5. Reconnect the power cord to a wall outlet and to the printer.

   NOTE: 

   HP recommends plugging the printer directly into a wall outlet.

6. Turn on the printer to complete the reset.

Follow the steps mentioned under "Troubleshoot a 'Paper Mismatch' message (Mac)" in this HP document for more assistance:- Click here

Let me know how it goes.

To thank me for my efforts to help you, please mark my post as an accepted solution so that it benefits several others.

Cheers.