binascii.error: preenchimento incorreto em python django
I'm not sure this applies to your situation, depending on where you're storing your encoded data.
I had the same error, but it related to some encoded session data. I cleared out the session data (cookies, cache etc) in the browser Devtools, and it fixed my issue.
Just posting this in case it applies or helps others who come along for the same reason.
Xenophobic Xenomorph