Flexbar could't identify Y base?

[HuaZou]

When I used this software to trim amplicon reads for 515F-806R primer, it reported the error as follows:

ERROR: Unexpected character 'Y' found.
Program execution aborted.

the following are the shell command and the primer sequance:

• command line

flexbar -a illumina_PE_adapter.fa   \
-ao 5 \
-qt 30    \
--min-read-length 180  \
 --threads 2  \
 --zip-output GZ \
 --max-uncalled 10   \
 -r /disk/user/zouhua/project/Hypertension_16s/Study/00.RawData/HTN1/FDMP20H002931-1a_L1_HTN1.raw_1.fq.gz \
 -p /disk/user/zouhua/project/Hypertension_16s/Study/00.RawData/HTN1/FDMP20H002931-1a_L1_HTN1.raw_2.fq.gz \
  --target result/02.trim/HTN1  \
2>result/logs/02.trim/trim_HTN1.log

• primer sequence

>forward_sequence_515F
CCTAYGGGRBGCASCAG
>reverse_sequence_806R
GGACTACNNGGGTATCTAAT

So I wonder that whether flexbar is suitable on trimming primer sequence ?