I think it needs to be formatted to fat32 before you can use it, if it's compatible with your R4 that is. Most people use this as windows own format tool won't do it. Or at least that is what I had to do with my R4.
Some carts, especially way older ones, can only read microSD cards. Yours may be able to read microSDHC ones as I recall that some original R4 clones have been modified to be able to read them. I'm not sure if there exists an NDS flashcart that can read microSDXC cards. Try finding another microSD card and use the Wood R4 firmware.
They do exist because I bought one as I tried to point out in my post. But it was a clone and a fairly recent clone at that.
People have been formatting larger SD cards as FAT32 for ages now. You can't do it with built-in Windows utilities, but tools like Minitool Partition Wizard will work. Even without that, I think you can just create a smaller partition that doesn't take up the entire capacity of the card.
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RedColoredStars:
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SylverReZ:
