If a tidal wave of Christmas romances and parade of second-chance-at-love pictures were no giveaway, “Purple Hearts” should be the Netflix warning shot that makes its point.

“We’re COMING for you, Hallmark Channel!”

A marriage-of-convenience dramedy about a Marine who could use some extra “marriage allowance” cash and a diabetic singer who needs insurance offers up the promise of conflict between a conservative soldier psyching himself up for a combat tour and an immigrant’s daughter, pacifist and would-be pop starlet quickly sours in a screenplay that loses its nerve and leads who have no chemistry whatsoever.

Arguments about “entitled” feminists and the “casual misogyny” of a “bro” culture military begin over-the-top, and are abruptly abandoned. With one Marine blurting, We’re good enough to fight for your ass, but not to touch it,” maybe that’s for the best.

Screenwriters Kyle Jarrow and Liz. W. Garcia and director Elizabeth Allen Rosenbaum skipped “Subtlety” day in film school. But not Schmaltz 101.

As they tell the story of waitress-and-aspiring singer-songwriter Cassie (singing actress Sofia Carson) and new Marine Luke (Nicholas Galitzine), everyone involved is charged with translating “Green Card” into a story of military insurance and benefits and “faking” a marriage until romance blossoms.

In leaving out the charm and the romance, and abandoning the picture’s “edge” to make it play for Hallmark Channel America, they pretty much blow it, even if scenes here and there work and deliver something like an emotional payoff.

Cassie and The Loyal — her band of waitresses and waiters — get the attention of Marines on leave in Oceanside, California. Cassie gets the attention of Luke, thanks to the fact that she’s not having this boys-will-be-boys grab-assing, and that she “used to babysit” Frankie (Chosen Jacobs), another Marine in Luke’s platoon.

The leads “meet cute” in a way that starts testy and practically leads to blows before they go to their separate corners.

But when Cassie ducks out to check her sugar levels in the parking lot, and take an insulin shot (“Type One”), we see her vulnerability. Not being able to pay for refills on her waitress/cover-band earnings, we get it. She’s facing a life-or-death medical problem that can’t wait.

An awkward “proposal” to old friend Frankie earns her a scolding from his son-of-an-M.P. pal Luke, “prison” threats and “scam” accusations. But then we see his vulnerability. Luke owes a low-rent mobster (Anthony Ippolito) money. Lots of it. He has a “past.” Cassie’s pitch just might work with him.

When they reach a bargain, we’re served awkward group scenes with his platoon, an awkward wedding and a seriously clumsy good-bye (after an abrupt night of passion), and he’s off. All she has to do is stay in touch, video call sweet nothings that the rest of his platoon sees, and get back to writing songs, only now they’re apparently inspired by Luke.

The character arc here is strictly Cassie’s, as the liberal “illegal alien’s” daughter comes to appreciate — slowly and clumsily — the sacrifice men in uniform make on this or that combat tour in the Middle East. “Purple Hearts,” from its very title, panders to corners of the country that hold military service in hallowed regard. Nicholas Sparks and others have gotten rich surfing America’s urban/rural/Blue State-Red State “sophistication gap.” Why not Netflix?

But most viewers, including me, will see through the movie’s ham-fisted manipulations and poorly-executed tugs at the heart strings.

Yes, a military funeral is all but guaranteed to draw tears. But every other emotion, every plot twist towards “love” and away from “convenience,” is handled so poorly you cringe.

Carson’s breathy singing voice is pleasant enough and very much of its time, even if the ballads she plows through here fit well only because so much of what surrounds them is also pure schmaltz.

Galitzine and pretty much the entire remainder of the cast achieve “adequate” in their best moments.

I wouldn’t have minded seeing a film wrestle with these real rifts in the culture, intra-generational gaps that have widened since the end of the draft. That sort of conflict could have set off real sparks and provided a basis for the chemistry our leads sorely lack.

“Purple Hearts” plays like a Cassie-gets-her-big-break wish-fulfillment fantasy with the whole fake marriage business, debts and medical issues and everything else mere afterthoughts.

Rating: TV-14, violence, sexuality, profanity

Cast: Sofia Carson, Nicholas Galitzine, Chosen Jacobs, Linden Ashby and Anthony Ippolito

Credits: Directed by Elizabeth Allen Rosenbaum, scripted by Kyle Jarrow and Liz. W. Garcia. A Netflix release.

Running time: 2:02