Hi fsgoodrich,
Please follow all of the steps on this page from the manual to clear the 1303 error you are experiencing with your PIXMA TR8520:
https://ij.manual.canon/ij/webmanual/ErrorCode/TR8500%20series/EN/ERR/1303.html?ref=1303
If the 1303 error persists, your PIXMA TR8520 would require service. If your PIXMA TR8520 was purchased less than a year ago, please contact one of Canon's Technical Support Representatives via phone or chat to obtain your in warranty options. To contact a Technical Support Representative, please use the link below to log into your My Canon account:
https://mycanon.usa.canon.com
Once logged in, click on your PIXMA TR8520 and then click on the Product Support button. When that page loads, click on either the Phone Support button or the Chat Support button to access support.
If your PIXMA TR8520 is out of warranty, you are eligible for Canon's Upgrade Program. This is for out of warranty units which have been diagnosed to require service, or for some reason are incompatible with a new or upgraded system. This option allows you a one-time opportunity to purchase a replacement product, discounted from the list price.
If you would like to take part in this option, please call our Sales Department at (866) 443-8002 Monday through Saturday, 9am to 9pm. Let them know you have been working with technical support and the Canon Upgrade Program was offered.
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