Good it works but I’m amazed the Flipsky support team didn’t give you the solution.
NO BEC = OPTO version, your pb is similar to Maytech OPTO 300 wiring diagram found here ‘Connections explained to a dumm newbie - #5 by Flightjunkie’
Splicing can be avoided using a Y cable like
https://www.amazon.com/gp/product/B07HF8D2WF/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
