Note: You might want to create FreeTheTree saved adverts backup before this operation as all data and cookies stored under the site my.gumtree.com will be deleted.
- Go to: chrome://settings/cookies/detail?site=my.gumtree.com
- Filter down to the my.gumtree.com
- Click remove data
The window might looks also like this one below
4. Go to https://my.gumtree.com/manage/ads and allow files to be stored on the site when pop up shows up.
Done 
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