Adding a new GDS node to my existing GDS file

[GabryS3]

Dear Dr Zheng,
I am trying to add a node to my GDA file, but I am struggling a lot with it, so I would love some advice and help with this.

I obtained my GDS file by converting a "genlight" object (R package adegenet/dartR) into a GDS file for SNPRelate with the dartR::gl2gds() function.
However, the GDS file has no sample annotation, and I would like to add this as I would like to run KING robust incluging the family.id field (geographic population or hybrids/pure individuals categories).

I have read your SNPRelate tutorial, but I am encountering troubles adding a gds node to my GDS object.
Here is the code I used:

"
mydataset_GDS = gl2gds(
mydataset_genlight,
outfile = "mydataset_GDS.gds",
outpath = getwd(),
snp_pos = "0",
snp_chr = "0",
chr_format = "character",
verbose = 5)

sample.annotation = mydataset_genlight@other$ind.metrics # contains all individual metrics in a dataframe format

class(sample.annotation) # data.frame

    mydataset_GDS_File= snpgdsOpen("C:/gabry/analysis/mydataset_GDS.gds", readonly=FALSE, allow.duplicate=FALSE, 
                                                              allow.fork=TRUE)
    
    class(mydataset_GDS_File) # "SNPGDSFileClass" "gds.class"     
    
    get.attr.gdsn(index.gdsn(mydataset_GDS_File, "snp.chromosome")) # NULL
    get.attr.gdsn(index.gdsn(mydataset_GDS_File, "sample.annotation")) #   No such GDS node "sample.annotation"!

    
    add.gdsn(mydataset_GDS_File, "sample.annotation", sample.annotation)
        **# Error in add.gdsn(Blacktip_Rep0.98_test_5genotypes_GDS_File, "sample.annotation",  : 
        # Invalid GDS node object (it was unloaded or deleted).**
    "

I don't know how else to include the sample/individuals metadata in the GDS file. I would really appreciate some help!
Thanks a lot!
Best,
Gabriella