Wallpaper not sticking

Without knowing the type of paper the most obvious answer is poor quality adhesive. If it is 'paste the wall' type then you might be leaving the paste too long before applying the paper. Or the paste might be either too thick or too thinly mixed. Alternatively you might have not given enough time for the paste to soak into the paper before hanging it. Lastly, have you sized the wall well enough first or is it bare plaster?

The wallpaper is only as good as the surface it needs to be applied on ,so if the plaster surface is shiny or has been painted previously it will need to be rubbed down with sandpaper first so you have a surface that will adhere to Always use Solvite paste as this is the best I have never had any problems with wallpaper not sticking with this product ,and with fresco you need to ensure the paste is mixed thick ensuring good adehsion

Some super Fresco papers require the paste to be applied to the wall and not the paper, did you read instructions fully? I am guessing that the adhesive is not strong enough or if you have mixed your own it is has too much water (loose). How you apply the adhesive can also be a factor, brush or roller.

Type of wallpaper matter the most, as well as the wall surface. If the wall is newly plastered it will soak way more paste so you need to paste it once with thin paste or a primer and leave it to dry, then depending on the wallpaper you have, you may need to paste wall and hand dry wallpaper or paste the wallpaper and leave it for a while to soak first. Look at the little icons on a wallpaper roll label to find out the type of the wallpaper you have and if you don't know what they mean, search in google ar ask here. Hope that helps!