Losing Credits during Cerberus and Baal battles

[ARMOR]

I've been using some credits for boost but it keeps saying it isn't available and wait 3 seconds but it still deducts credits from my collection. How is that possible? I mean i end up spending 10x the amount for no reason. This has happened several times.

Or am I missing something in that if you use credits it is not guaranteed to work your boosts?

[Elke-Sarah]

Or am I missing something in that if you use credits it is not guaranteed to work your boosts?

That's correct, iirc the word "chance" is in the mouseover tip. Gems always give the boost, credits only give a chance to boost. Getting the 20% boost costs 20k credits per attempt, or 2 gems. After that, getting the 40% boost costs 40k credits per attempt, or 4 gems, etc.