Boolean FMI parameters

[ClemensLinnhoff]

I am trying to set a Boolean FMI parameter for an FMU in the config yml. I tried different variations: True, true, "true" but I always get the following error:

channel is ready for work
Unexpected error in RPC handling
Error in initialization of simulation interfaces.

Setting string or Interger parameters works. How do I set the value for a Boolean parameter. My concrete example is the OpenMSL Network Proxy FMU.