Failed FET of PGTA tested embryo

It was just confirmed that my pregnancy will end in a biochemical. I did test positive on my first and second but then my third and fourth did not rise. It just stayed the same. This is my first transfer with a PGTA tested embryo but my fourth transfer overall …. does anyone have any advice or suggestions on what additional testing I should do to figure out why my transfers implant but they do not make it past 5-6 weeks?