Huge day in court for Robert Kraft ... the State of Florida is trying to convince an appeals court to ALLOW graphic video shot from inside a Jupiter day spa to be used against Kraft in his sex acts case.

It's all happening right now -- and it's all being live streamed.

Remember, prosecutors say cops got a warrant to secretly install cameras inside the spa because they believed it was operating as a brothel ... and they wanted to catch criminal activity in the act.

Cops say they have footage of Kraft at the spa on 2 different occasions in 2019.

But, in a previous ruling, a judge ruled the video was NOT permissible because law enforcement did not do enough in their surveillance to protect innocent people who were inside the spa getting perfectly legal massages.

The State of Florida has appealed that decision -- and now a panel of judges in the Fourth District Court of Appeal (located in West Palm Beach) will decide if the previous ruling will stand.

Jeffrey DeSousa is representing the State of Florida. Derek Shaffer is representing Robert Kraft.

DeSousa claims the video of Kraft, specifically, was shot legally -- and prosecutors should be able to use the footage to prosecute him ... claiming its essentially a smoking gun.

As we previously reported, Kraft was busted back in Feb. 2019 after officials say a sting operation at a Jupiter, Fla. massage parlor revealed the New. England Patriots owner did illegally pay for sex acts on at least 2 occasions.

Originally, the video WAS to be allowed in the case ... but Kraft's dream team of attorneys successfully argued at a series of hearings last year it should not be permissible.