Let's look at Baidu Encyclopedia "gravitational redshift" entry https://baike.baidu.com/item/%E5%BC%95%E5%8A%9B%E7%BA%A2%E7%A7%BB/ 946741? fr = aladdin introduced,
implied in the text:
"Before Einstein's general theory of relativity is completed, he had come to gravity will affect the light wave frequency and wavelength conclusions due to the effect of gravity, when traveling up and away from the surface when the light waves will lose some energy, longer wavelength, frequency decline."
So, the photon energy loss occurs, gravity is acting up? But gravity is curved space, work space will bend it?
In addition, the loss of photon energy gone? What transformed into energy? Transfer gone?