Klaviyo: Email Marketing & SMS

It's crap. We chose Klaviyo because it can create coupons and activate upon sending the email, 22% of the times it didn't work (we have 3 shopify-linked Klaviyo account, all experienced the same). Contacted support, and the problem was never solved, they just say "it's hard to say why it didn't work..." ????? Seriously?
The upside is, the onboarding manager and account manager was very helpful and nice.