Currently foreign tokens that have a number of fractional decimal places that is not equal to 10, the number used by the native token ZTG, cannot be processed in prediction markets as the fixed point math used is not capable to handle numbers with different numbers of fractional decimal places.
The proposal at https://hackmd.io/@lZVVinJVS6WI4IpRgmbsLA/Hyz0dJXFn describes the solutions and the recommended approach to deal with this issue, effectively paving the way to use any token in prediction markets.