Increase internal memory of Samsung J2 prime
Try formatting the sd card as ext2, default sd card storage type is fat32 i think?, the android may not recognize it as a usable sd card, now a notification may appear saying : (SD CARD NAME) is not recognizable, it need to format or something close to that, a option may appear: Format as INTERNAL STORAGE and Format as PORTABLE STORAGE, pick the "Format as INTERNAL STORAGE"

EDIT: I think your android was flashed because of bootloops, i dunno?, It remove the option to format as internal storage