The front and back of my bed have a 0.4mm difference which is making the fillement not stick on the back.
The troubleshooting guide only talks about tight or loose screws which didnt make any difference for me.
Any good ways to level the bed on this printer?
I had the same problem with my printer. The only “solution” I’ve found is to place a few layers (in my case, 2) of paper between the “back supports” and the bed. This made the back of the bed rise enough for a level printbed.
Not the best solution, but it works 
And now I realised that there is an actual solution here:
https://manuals.velleman.eu/article.php?id=676#BED_NOT_LEVEL
How did you solve your problem?
I probably need to level the X rods in the back but they are fixed with the holders so there is no acctual possibilities of leveling of them.
My bed is too low in the back and even more in the Home posistion far to the left.
(Thinking of cut the stripes and fit something under the rods and fasten them again or make the holes on the sides oval to be able to adjust the plastic rod holder up or down and place som spacer or something against the top to make it firm.)
Anyone having good ideas how to solve this?
Earlier I used the “pieces of paper” solution mentioned above. The manual I linked have have a solution; “THE PRINT BED IS NOT LEVEL”. I did not have time to use that solution with a new testprint because I had to send my printer to my local suppliers repair shop for an unrelated hardware problem.
I would also suggest to check the assembly instructions to see exactly how the rod holders are supposed to be mounted and compare it to your own printer https://manuals.velleman.eu/article.php?id=516
I bought the pre-assembled version and had a bit of trouble with loose screws that had to be tightend (some are supposed to be a bit loose though, like for the Z-motor).
Well… this printer is giving me nothing but a SEVERE headache!!! 
The manual is not helping, at all. I have been working for several hours to try to get the bed in straight level across the whole printing surface but to no avail. It’s like the problem is diagonal and I can put as many papers between those rubber stands under the plate I’d like but it will still be to high on one end and to low in another.
I manage to update the firmware to Marlin 2.0 but it does not help much but you will get the possibility to change ALL axles within 0.025 - 10mm steps. That is a very welcome feature while calibrating!! 
But be aware! The nozzle tends to crash into your bed when doing first calibration.
Is there any good recipe for a solution to this other than rip this miserable peace of…dysfunctional apparatus apart and selling it’s limbs for food to my children? 
(I will not let it win over me!There must be a way to make it leveled! 
)