All telescopes, refractors, reflectors, and catadioptrics, as well as all cameras, have inverted images because that's the way all lenses and mirrors work. ... When a “star diagonal” is used, the image will be corrected right-side up, but it will remain backwards from left to right.

How do you fix an inverted image in a telescope?

One of the biggest surprises that beginner astronomers have is when they find that the view they are seeing through their telescope is upside down or backward. To correct upside-down viewing equipment known as a Diagonal can correct the image and turn it right-side up.

Is the viewfinder on a telescope supposed to be upside down?

There is nothing wrong with your finder scope or your telescope. The images will appear upside down and reversed left to right. This is normal. You can use a correct image diagonal to make the field of view appear the way you would see it with your naked eye, but it's really not necessary.