HELP!!! Making External Subs on Oppo 203 Work!

[Filmmaker]

I dunno, maybe I'm an idiot but I have tried and tried to follow online tutorials and I cannot seem to make external subs work on my Oppo 203. Here's where I'm at: I'm on my third attempt at subscene.com for the 2020 movie ALONE (the one with the woman stalked by a psycho, not the global pandemic one). After a couple of other dead ends, I've settled on a file named "alone-2020-1_HI_english-2365730" that purports to be ripped from the U.S. Blu-ray (I'm attempting to add English subs to the German BD). I have created a folder named "sub". I have moved this subscene.com file into the sub folder and renamed it "sub.srt". When I play the movie back and select the subs menu, it now has "Other" as an option so I know it's detecting the file on my flash drive, but NO TEXT EVER SHOWS ON THE SCREEN. I've tried this with three different files now. What am I doing wrong? Please, someone show mercy and guide me through this like I'm a five year-old.