Render Texture in Render Texture not Rendering?

Mouthful of a title. Anyways, I am trying to make a mirror in mirror effect by having two mirrors face each other. I attached a camera on each mirror, facing each other. Then, I made them respective render textures, and assigned their cameras onto those render textures. Simple stuff. However, the mirror won't reflect infinitely. Instead, it shows the opposing mirror as totally black. The render texture is working, but the render texture is not working IN the render texture. Attached is an image.

Not sure which settings to tinker around with here.

Using URP.