After the development my negative strips are all transparent and there are no pictures or only slight shadows to watch ?
This can be due to several things.
One of the most common reasons is underexposure. A typical beginner’s mistake is not removing the lens cap when taking the picture. How to fix this should be clear.
Another reason could be that there is simply too little light on the film. This is often underestimated, especially with Holgas and Dianas. Especially the toy cameras have a rather small aperture, a low-sensitive film (ISO 100) and if you take pictures in the evening or indoors, the result is quickly non-exposed or underexposed pictures.
Also the use of a flash does not always help or the flash provides enough power for the desired picture. With the typical toy cameras one should rather shoot in sunshine, especially with films with a low ISO number.
Of course it can also be due to the reason that the chemistry did not work properly during the development. But this is very unlikely if you have it developed in a large laboratory.