VarSome Clinical accepts any VCF file, however it must conform to the standards for VCF files. The issue is usually a malformed header or a missing header.
You may use one these validators:
Basically, the VCF file needs to follow the VCF standard correctly. Another quick test is to just see if a standard program like bcftools (https://samtools.github.io/bcftools/bcftools.html) recognizes the file and doesn't complain.