issues to use bcftools isec to compare two different .vcf files

Hello everybody. I am not an expert in bioinformatic I just use Galaxyfor my project. I am getting an issue when I am using bcftools isec to compare two .vcf files. I do not really understand what should I add in the -p parameter boxe. I really appreciate it if can give me any advice!

Fatal error: Exit code 255()

Expected the -p option