I have to send my (Nintendo Switch) Joy Cons in for repair. They gave me a prepaid UPS Ground shipping label but I was on my own for packing materials.

I packed the controllers into the box my phone came in, then put that into the padded envelope. I thought it was decent-ish, until I closed it up. Now it seems misshapen and sketchy.

Would UPS accept this? Or should I start over (and buy a box, I guess)?