RB67 question for the old timers.

I recently purchased a “50mm SEKOR” lens for my RB67 Pro S and cant seem to get the shutter to function. Could this be due to a faulty shutter or may this lens not be compatible to the Pro S body?

I have two other lenses; both function well and both are “SEKOR-C” lenses. The “Sekor 50mm” dose not have the “C” designation although it mounts on the body.

I was billed a costumes fee too have the lens shipped across the boarder to Canada which may not be recoverable, if I were to return the lens to the seller. Having it repaired may be my only option if it is indeed compatible to my system.
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A.M.H.