the code specified = *21 (the 10 digit number to reach ) # gives an error "Error performing request / unknown error".
Can I request this call forward through the Fido website rather than through a simm card that is inoperable in the new country?
Welcome to the community!
Unfortunately, I don't think what you're trying to do is possible. As far as I am aware, calls can only be forwarded to Canadian or US phone numbers
While Barbados might share the same North American Numbering Plan (ie Country code: +1), they are not a part of the either Canada nor US. They are an independent British Commonwealth nation.
That said, depending on your plan, your SIM should be operable in Barbados as Fido does offer Fido Roam to that destination:
~taken from here.
If your SIM isn't working, you might consider contacting customer service to verify there are no roaming blocks on your account. If you rather using your roaming services on a pay-per-use basis, you would need to contact customer service to opt-out of Fido Roam. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they'll also be able to access your account.
Hope this helps 😀