This project was flawed from the beginning. Mother Nature always wins.

Were you trying to avoid having steps?

A walkway to where .? Of course the rain washes it away . I need more info but this was a bad idea from the start. You need to show more of the space so I can see what you wanted from a walkway there

Ok I’ll add some more photos tonight- the walkway is to a shed that was placed at the top of the slope- it may have been a bad idea but I have to live with it now and find a solution

I need to avoid steps as I store my lawnmower in the shed

Concrete or pavers. Ask the installers if they can re-use the decomposed granite as a base. The pavers may let some water soak in between them. The concrete may make a smooth channel for water to run downhill, so consider where you want the water to end up at the base. A small channel or gutter to one side may help direct the water.

Hers another photo from farther back- you can see the elevation of the area where the shed is. We did try adding the polymeric sand to harden but the rain was too much. The job was done by a person who is an all around handyman in the yard. But I think this job requires some technical expertise.

Dumb question-how do you lay cement on a slope without it flowing away before it hardens?

Wet concrete is not liquid, but it’s a little looser than peanut butter. A professional installer can watch to keep it smooth as it hardens.

I would figure out where the water is coming from and deal with it with something like a French drain.

Rainwater will follow the path of least resistance to the lowest possible point.

If you can get the rain water to wash OFF your walkway to one side almost as soon as it lands, it will not build up volume and speed and wash our walk path away IF it runs off the walk path in the direction it ultimately wants to go and does not need to again cross the path to get there ... as yours, unfortunately, appears to do at the low left point.

As the rain water flows downhill, it builds up volume and speed. Spaced stones can help slow the speed. Getting the water off the walk path as after it lands as possible by having a sloped walk path can keep the volume of water lower. Outlining the sides of the path in stones on the low end and adding stepping stones within the gravel path can help with that.

To the left of your structure, it appears your path is sloped toward the middle area the structure if facing. Because the low point of that center is above a subsequent curve in your path, the water will need to cross over or under it again.

Could you use the same kid of wood used for your deck and create a small bridge at the lowest point of your path to let the water pass under there? Literally scoop a low place below the low place and add pavers or rock so only their tops show to "pave" the scooped area. and build a small bridge over it.

https://www.google.com/search?q=small+wood+bridge+over+drainage+ditch/creek&client=firefox-b-1-d&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjRhb3B5tjvAhVHTt8KHXvNCtoQ_AUoAXoECAEQAw&biw=1366&bih=626

If you can build that bridge, you don't need to otherwise change the path of the walk path -- you need only to stop the wash within the path. That likely could accomplished by outlining the low SIDE of the path with brick or ricks or pavers or stepping stones to keep the rock within the path. Then, within the path, at any place where you see a wash begin, add a stepping stone to slow/turn the water off to the low side of the path before it can wash farther along/with/within the walk path.

How many stepping stones and where you will need them placed will depend upon where the washed places are.

https://www.homedesigninspired.com/lay-a-stepping-stones-and-path-combo-to-update-your-landscape/ 

Since your stones are so heavily sloped, it might well be a good idea to actually seek to get a grass or ground cover growing between your stepping stones.