Flooring problem

[billozz]

. Can anyone help please the guy that did the flooring used fibre board under it but seems to have missed a bit, the floor slopes from the front of the picture to the rear and I'm not sure how to fill the gap so that it's level. I have to do it myself as I can't get the guy now it was done a couple of years ago.
Thanks

 

[foxhole]

You are looking at problem back to front, the floor needs to be level before anything is laid on it.

 

[dazlight]

As Foxhole says. Needed prep 1st of smoothing compounds

 

[billozz]

What can I use to level the floor in that gap please

 

[dazlight]

Ardex rapid repair A45