Soft start/easy start

Hi
New to the community. I have 2 AC500’s, with 1 ac500 which has 1 300 k and 1 300s battery setup

The other ac500 has 2 300k batteries. It runs the home ok, except I cannot get it to start my heat pump, which is A/C also. The fan kicks on but the unit will not produce heat. I have a 50amp breaker, when I kick on A/C it throws the breaker. I have used a 12000/9000 watt gas generator with NO problems. Kicks either A/C on, or Heat pump and does Not throw the breaker. Do I need a soft start hooked up to heat pump?

@vincekoll
The reason it can’t carry is that the current is too high during startup. Soft starting allows the current to rise slowly, but it doesn’t guarantee effectiveness. There is still a possibility that the actual current remains too high after use.