Justin Bieber Cancels Montreal Appearance -- You Wanna Play, You Gotta Pay

8:15 AM PST -- A rep for Beachclub tells TMZ ... "We are incredibly disappointed and upset by the lack of professionalism exhibited by Team Productions (the event's promoter) in violating their contract with Justin Bieber and disappointing the thousands of fans that were going to flock to Beachclub today."

Justin Bieber has pulled the plug on a big event in Montreal Saturday, but only after the handwriting was on the wall -- the promoter wasn't paying him ... sources connected with Justin tell TMZ.

Bieber was scheduled to host an event at Beachclub, where he'd sing one or 2 songs and press the flesh. It's the same club where Kylie Jenner celebrated her 18th birthday and raked in $200K.

Our sources say according to the contract Bieber's team signed with the promoter, they would pay Justin 1/2 of his appearance fee when the contract was signed and the other half 2 days before the event. We're told the contract was for "a couple of hundred thousand dollars."

We're told Justin got the first half but Thursday came and went but the balance never showed. Our sources say Justin's people contacted the promoters and were promised payment pronto, but it didn't happen.