Light Barrier

During your Standby Phase, toss a coin. If the result is Tails, the effect of this card is negated until your next Standby Phase:
● When you Summon an "Arcana Force" monster, choose which effect to apply without tossing a coin. If an "Arcana Force" monster destroys an opponent's monster by battle, you gain Life Points equal to the destroyed monster's original ATK.

When I put this card during Main Phase does it have the effect cuz the coin flipping is on next standby

yes u do get the effect if u activate this card during your main phase or battle phase. However if u wan an easy way to keep this card with its effect, u can just have a splendid venus on the field, and even if the field card negates its own effect, splendid venus would negate that, resulting in your field card having its effect regardless of coin results