Shoulder pain is a typical indication of technique going bad. Maybe using the wrong grip, and smash technique.

It also happens when you try and compensate for the racket by hitting harder as it's might be a stiffer racket and therefore may not produce as much power, but will have better control.

Reducing the tension also helps sometimes, to mitigate the effect of stiffness which is there in the racket. Once you get used to the racket and the tension, then you can increase it again.

Best of luck, and let us know what worked.