will it work if we purchase a SC GC instore?
According to t&c, it only works for new membership, not any other purchase.
It does not say limit 1 per account
Well you posted the t&c. And it said limit 1 per American express card. Not per account
then what does this mean? "across all American Express offer channels"
Whether you got it via Twitter or on the Amex site, etc.
If trying a regular purchase, i think you should only out $45 on the card with the offer. Just in case they somehow know to credit only a $45 charge.
It's 45+ taxYou can also buy the expensive membership (which is about $100 +tax) And tax will vary based on state