Hey there @roushrsh
Where did you purchase your new Fido SIM card from? When you buy it in store, the change should be processed on the spot. That being said, you should also be able to complete the SIM card change online on Fido.ca.
Would you be able provide more details on the error? What's the content of the message?
Let us know!
Welcome to the community!
Are you trying to change the SIM card for a Postpaid or Prepaid account? If it's for a Prepaid account, it might only be able to be activated in a Fido store (see here).
Hope this helps