There's a load of similar TB6560 boards but one on Ali Express said this;

"Relay spindle interface - Outputs Max. 36V 7.5A for spindle motors or coolant pump (only one device can be powered by this output!) "

It already had a relay on board but if you say it also needs another external relay then that's fine but like JAZZCNC said if you are using the wrong terminals i.e. NC instead of NO you will maybe have the same problem once it's connected up.