The error indicates that the file contains invalid lowercase characters. You could convert these to uppercase to continue, but there could be other issues with the file if you are trying to use data that have already been processed.
I would recommend starting with the raw data. The raw data for this study appear to be deposited on SRA:
so you could download and automatically format the data from there using the QIIME 2 plugin q2-fondue:
This might be an easier approach, as you could then also follow the QIIME 2 tutorials from the start instead of figuring out the entry point for starting with FASTA data.
When using 'fondue', may I enter GSE number in 'NCBIAccessionIDs'?
And in the tutorial code, what should I put in the 'metadata_file_runs.tsv' part instead? The only files I can get from GSE162844 are the taxonomy file and the fasta file.
I'm just starting bioinformatics analysis, so I think I'm asking a very basic question, but I'm curious about this part. Please, reply.