It is not normal to have wrist pain while playing the guitar (of any kind); often the cause is the wrong playing posture. We have looked at guitar playing posture for acoustic / classical and flamenco in a previous article which we suggest you briefly watch the videos for before looking at the below.
Why? Because the way you hold your back and sit will affect the placement of your wrists.
Left Hand Technique to Avoid Wrist Pain
Best explained in the video below – in brief you want to be placing pressure on the strings as lightly as possible. Your hand should not be a clamp applying so much pressure that your hand clams up and your fingers are vibrating with tension. Your hand should be loose enough that it can glide up and down the strings. Your hand should almost not be supporting the neck of the guitar – which is covered by your seating position and your right should (see later). This leaves your left hand free to glide up and down the fretboard.
Right Hand Technique to Avoid Wrist Pain
This is the more common complaint about wrist pain. Review the first 30 seconds of this video to see how the right arm should sit across the body of the guitar, and how loose Rafael's hand is. If you are not a flamenco player specifically, you can ignore the rest of the video discussing the rasugueos of flamenco guitar.
One key thing to note is how 'light' the right hand should be on the strings, when the thumb or fingers are sitting on them. They should not be 'weighing down' or bending the string, but just loosely sitting on top of them:
To illustrate this point about wrist tension, review a common student mistake in right hand technique below, and how Rafael corrects it:
Finally, don't forget to warm up your wrist and right hand fingers before playing – Rafael uses a sponge to mute the strings: