When you target a creature that’s concealed from you, you must attempt a DC 5 flat check before you roll to determine your effect.
The concealed condition doesn’t change which of the main categories of detection apply to the creature.
So you could also be Hidden:
When targeting a hidden creature, before you roll to determine your effect, you must attempt a DC 11 flat check.
Ok, it doesn't make sense to me that you'd have to roll 2 flat checks, but I don't see why not.
Sorry if this is obvious, been a long week.
They have a rule for that.
Flat Checks
When the chance something will happen or fail to happen is based purely on chance, you’ll attempt a flat check. A flat check never includes any modifiers, bonuses, or penalties—you just roll a d20 and compare the result on the die to the DC. Only abilities that specifically apply to flat checks can change the checks’ DCs; most such effects affect only
certain types of flat checks.If more than one flat check would ever cause or prevent the same thing, just roll once and use the highest DC. In the rare circumstance that a flat check has a DC of 1 or lower, skip rolling; you automatically succeed. Conversely, if one ever has a DC of 21 or higher, you automatically fail.
There's the obvious answer I knew must exist! Thanks muchly!