Use SBI Yono Gyftr. It has usually had even Amazon Pay vouchers at 1-3% off in the last few weeks & it does give the double dip of extra 5% via the CB card.
In my case, card was blocked for my first attempted txn last month. Got it unblocked via the automated call which comes. After that there's a recommended cool off of 24 hrs which I waited.. post that luckily haven't had an issue with card blocking. Did 3 successful voucher purchases in the last 2-3 weeks.