The verification is by your bank, not Garmin. Garmin can't dictate the verification mechanism nor solve a SMS problem.
Apparently the varification comes from Garmin, I have just spoken with a representative from Revolut and they confirmed this. I have requested the SMS multiple times but didn't receive it.
I have the same problem here in France. Any solution to the problem as yey?
Curve (my card provider) eventually solved this. I'd been suspicious about my mobile number format in the app (about whether or not the initial zero required for a UK national number, but dropped in the international format) and updated that. However Curve advised that while this was the issue, for some reason they had to update it themselves to make it work.