O.K. Heres my problem. Previously, I had a 240 volt hot tub with a
50 amp Double pole GFCI. Recently replaced hottub with a 240v sauna.
Now, according to the wiring schematic. I need one 240v line hooked
up to power the three heating elements.

Unfortunately, the power coming off the GFCI seems to be on 110v ( 2
lines 110v each = 220v). This is a four wire hookup ( black, red,
white, ground). It seems that I need a 3 wire hookup for the sauna
( black, white, ground). However, no matter how I wire this sauna
heater, I seem to be only getting 110v to the elements.

Went to local hardware store and bought a 40 amp 120/240 v SINGLE pole
breaker was told that that the breaker should recognize whether the
appliance needs either 110v or 240 v and would give accordingly.
Unfortunately, when only hooking up, I still only receive 110 v to the
heater according to both my multimeter and a simple circuit tester.
Out of the 4 wire going to the sauna, I only hooked up black, white,
and ground, and just left the red dangling.

Am I missing something here? Is it possible to force 240v out of
single wire hookup? If so, how? Thanks.