converting annovar-formated vcf files to bcf files

Question

[hrora]

Hi, im trying to convert an Annovar-formatted (converted) VCF to BCF, so I can later merge the resultant bcf to a much bigger BCF file which contains the information on a big patient cohort. I get the following error:

bcftools convert -Ou 225_annv.vcf.gz > 225_S31.bcf

error: Failed to open 225_annv.vcf.gz: unknown file type

any suggestions? Thanks