Resurrection has a few relevant properties here.
- Casting the spell has a material cost of a diamond worth at least 1,000 gp, which is consumed.
- Casting the spell requires expenditure of a 7th level spell slot and 1 hour of casting time.
- The creature that is restored by a Resurrection spell has a -4 penalty to attack rolls, saving throws, and ability checks. The penalty is reduced by 1 each time they finish a long rest.
"Free" as stated on the certificate isn't clearly defined literally anywhere in the rules, however you can consider other effects in-system that are similar. For example, take this excerpt from the Wish spell, emphasis mine:
The basic use of this spell is to duplicate any other spell of 8th level or lower. You don't need to meet any requirements in that spell, including costly components. The spell simply takes effect.
"Wish", PHB p 289.
You can reasonably assume that Wish grants you a "free" 8th level spell or lower. It does not give you the power to cast the spell, and you are not casting that spell after successfully casting Wish. You just get the results of the spell you chose. No casting means no casting time, and no components.
The wording of the certificate reward mentions nothing about casting the spell. You're simply entitled to one free Resurrection (capital R). The intent here is to give you an opportunity to restore a dead PC, but still bound by the rules of the Resurrection spell's effects, I.E. the penalty to rolls. This means you can't just recklessly dive into the BBEG's fireballs and tank them with an extra life, but it does mean you get a mulligan if your PC meets an untimely demise.
You are in a good position being the DM asking this question and not the player. Ultimately, it is up to you how to implement any undefined details such as this. From the DDAL FAQ:
As a D&D Adventurers League Dungeon Master, you are empowered to adjudicate the rules as presented by the official materials (PHB, DMG, MM, etc.). Run the game according to those rules, but you are the final arbiter of any ambiguities that might arise in doing so. - "What Rules Do I Use", DDAL FAQ v6.0 pg 3.
As always, the DM remains the final arbiter of how a rule is to be implemented in their game. - "What about Sage Advice?", DDAL FAQ v6.0 pg 3.