Mupen64 Emulator Transfer Pack with Pokemon Yellow

Because my item bag is full i tried to use the Pokemon Stadium which is on N64. So i google for Transferpack which is needed to connect Pokemon Gameboy game. So i found Mupen64 but i don’t find the Transferpack function in Retro Arch (is Mupen 64 a lite version on Retroarch ?)

Anyway: I donwloaded Mupen64+ FZ for Android on the App Store directly and there the option is available. And there i have to choose the ROM file and the RAM file (what is a RAM file ? Savefile?) I selected the ROM-File folder and the.gb file and for the RAM file i selected thesavefile in .srm

And it worked for the first moment. I transfer the items in the Pokemon Stadium game, went out (it asked me to safe, i did) and then i went out and it doesn’t safe.

So why did it not save ? Has the Mupen64 app no write-right in the retroarch savefilelocation ? Because it worked, when i reopen the menue in the pokemon Stadium game, the stuff was trasnfered, but when i start the game in retroarch, it’s still the same savefile??