I keep getting ERR.021 when trying to download tax slips from CRA. Is there anything I can do beyond waiting 4 hours on the phone for a CRA agent?

Unfortunately, that error is coming from the Canada Revenue Agency (CRA), so you will need to contact them to resolve your issue.

If you are in Canada or the United States, you can call the CRA at 1-800-959-8281. If you are elsewhere, you can call 613-940-8495. This CRA page, “Contact the Canada Revenue Agency”, has more ways to contact the CRA.