I have multiple fastq files like this:

TK273759_R1.fastq
TK273760_R1.fastq
TK273761_R1.fastq
TK273762_R1.fastq
TK273763_R1.fastq

I used this command to subsample 500000 reads from those files:

seqtk sample -s100 not_bear_dna/{i}_R1.fastq 500000 > subsample/{i}_R1.fastq

I get this error:

[E::stk_sample] failed to open the input file/stream.

I am not sure what I am doing wrong here, it works for a single fastq file but not for all. Here's my command when I subsample from only one fastq file:

sample -s100 not_bear_dna/TK273759_R1.fastq 500000 > subsample/TK273759_R1.fastq

I appreciate your kind help!