John Hinckley Jr. says his music career keeps hitting the same sour note ... venues book him, fans buy up the tickets, and then the whole thing gets canceled.

And, well ... it's not exactly hard to figure out why.

The man who shot then-President Ronald Reagan in 1981 opened up about his trouble getting onstage in Episode 2 of "The John Hinckley Podcast," telling guest Lola Pepper that clubs and music venues repeatedly pull the plug because of "who I am."

Hinckley says venues will start selling tickets to his shows -- and he claims they'll even sell out -- only for the venue to yank the gig before showtime.

According to John, it's happened "about 10 or 15 times" ... leaving him feeling blacklisted from the live music scene.

Lola called the situation disappointing, and John agreed ... though, given his history, venues getting cold feet probably shouldn't come as the biggest shock.

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As TMZ previously reported ... Hinckley just launched his new interview-based podcast and has already floated one dream guest -- Jodie Foster, whom he says he'd love to have on the show.

John's convinced he's the reason Jodie is sexually attracted to other women ... so it's a good bet his dream of interviewing her will get shot down too.