drill batteries in series with Flipsky 75100

Hi friends.

I have an idea about electronics but Im new in BL electronics.I need some help to connect 2 makita bateries in series 18+18=36V with Flipsky 75100.

When i connect one battery 18volt everythink works fine with vesc tool, https://flipsky.net/collections/electronic-products/products/flipsky-751... and  ,motor https://flipsky.net/collections/waterproof-motor/products/5062-160kv-bru... connects and all working perfect.

But when i connect 2 batteries in series Flipsky 75100  , led flashing blue and red, and setup Foc motor failed.

I have to make any other configuration? or  Flipsky 75100 can not handle batteries in series?

Any help would be greatfull!!!