@JosePP Did you manage to fix above mentioned WHMCS issue? I'm experiencing the exact same error when I'm accepting new order on WHM ticking Run Module Create.
I've noticed that in some servers, this service doesn't start automatically when you reboot. Do you know why this can be or if it has already happened in some server?
@azlanirda in this case you need to check the domain log why it is generating 500 internal server error.
if you can post the log entry here we can get an idea.