New to me 10 year old TC 270 Domyos treadmill slipping

Hoping someone can advise. We've just bought a 10 year old TC 270 Domyos treadmill. We used silicone lubricant on it (it was confusing as the manual said it didn't need lubricating, but when we looked up replacement belts it came with the lubricant) and walked for about 5 minutes to make sure it settled. It's perfectly ok walking on it but I then tried taking it up to running speed and my feet kept slipping. I'm wondering what it could be. Could it be that we've lubricated it when it didn't need it, do I need more grip on my trainers, or does it need a new belt? On visual inspection, the belt appears to have grip (it has texture rather than smooth or shiny). I haven't a clue! Thanks