Unable to backup tokens from FreeOTP 1.5

[lcw0622]

hello everyone, I met a problem is that I can't backup tokens from old version(1.5).
As I searched, to back up data from FreeOPT Android, need such 3 command

# get backup data
./adb backup -f ~/freeotp.ab -noapk org.fedorahosted.freeotp

# conver backupdata to gnuzip
dd if=freeotp.ab bs=1 skip=24 > compressed-data 

# convert backupdata to tar
printf "\x1f\x8b\x08\x00\x00\x00\x00\x00" | cat - compressed-data | gunzip -c > decompressed-data.tar

but when I exec 3rd command, I found this error:

gunzip: invalid compressed data--crc error

so that I can't get final json file.
anyone can help me please? it's important for me, thanks

I'm not good at English, I'm very sorry if you feel bad when reading this issue

[pchtsp]

I confirm I get an error when trying to interpret the backup. Also, the file from the backup (first step: freeotp.ab) seems suspiciously small.