There are two incompatible interpretations of the redshift:

1. Einstein's: The redshift is due to a time dilation/contraction
independent of the gravitational field but dependent on the
gravitational potential, on condition that the speed of light is
constant in a gravitational field.

2. The redshift is due to the VARIABLE speed of light in a
gravitational field, in accordance with f=V/lambda, where V is the
speed of the wave.

The latter interpretation can only be incorrect if:

A) the formula f=V/lambda is wrong for light

B) lambda changes with the gravitational potential so as to satisfy
Einstein's time dilation/contraction

If f=V/lambda is correct and lambda does not change with the
potential, the principle of constancy of the speed of light is wrong.
General relativity would not be able to survive either.

Pentcho Valev