Starter has 2 circuits. One circuit is the starter control for crank and terminate commands. The other is the high power cranking circuit that does the work during engine startup.

There should be voltage at the large battery cable to the starter all the time (same as battery voltage). If not, then you are not getting power to the starter high power cranking circuit.

With the key switch in the start position, check for roughly 12V volts at the starter solenoid switch terminal. If not, then the problem is somewhere in the control circuit and not the starter.

If those pass then replace the starter or have it repaired.