The camera you are using adds about 45mm to the focus point.
You may well be able to get perfect focus with any eyepiece you have but the camera will be out of focus if the focuser can not go that far (45mm) down so your sensor is at prime focus.
The best way to find prime focus is to point the scope at something bright like the moon and take your eyepiece out. Then focus the moon onto a piece of paper. You should see a small moon on the paper at the point of prime focus. This is where your sensor will need to be.
Now you need to add the space for the camera and the adapter. This is generally around 45-50mm. If your focuser will not go that much further down towards the primary mirror then you are out of luck. It will not focus at prime focus for your camera as is.
So what can you do if you have this problem. The short answer is not much but there are work arounds. Some people have shortened their telescope tube by 4-5 cm and found it helps. But I assume you probably want to avoid cutting the tube if you can help it.
You can try eyepiece projection. Often you can find some eyepiece project or camera adapter have what is called a no piece adapter. It basically has a 1.25" tube on one end and a camera type thread on the other. The trick is that many of these are threaded.
You can obtain some thin eyepiece's where you can unscrew the shiny 1.25" tube. Then you can screw the eyepiece into the no piece adapter and wallah a nice eyepiece projection set up with very little if any space lost. Hence you will find many t will focus with a range of different focal point eyepiece's.
I use this often and it works. Though you use some light due to the projection. Well it is better than nothing.
Otherwise try obtaining a CCD or specialised camera. Though I suspect you want to keep the cost down.
I have simply obtained an eyepiece project kit that included the no piece bit. Then I unscrewed that bit and that is what is now in front of the eyepiece. You can add extension tubes for your camera if you need them or you want more magnification.
Not every eyepiece will fit inside a standard extension tube so if you want to use a particular eyepiece you may need to make your own tubing for it. Not particularly hard to and you can purchase tubing if you want or make it out of thick cardboard be it not as strong.
Good luck.
