The heartlandforest.org website does not host this form. Some adblockers or browsers are known to prevent cross site scripting. You could try the direct form link instead.
https://www.canadahelps.org/en/dn/8117

If you experience any issues with the transaction. Contact the phone number at the bottom of the error message to let CanadaHelps know if there is an issue they can help you fix.
Some credit card providers are known to block donation sites like CanadaHelps and will require you to contact the number on your card to unlock your card.