Error in set knots50 and knots100

[Xiangjun-Qi]

I have encountered the following problem in setting up knots. Is there a proper way to solve the following problem?

knots50 <- fields::cover.design(scale_expos, nd = 50)$design
Error in fields::cover.design(scale_expos, nd = 50) :
Error: R must not have duplicate rows

knots100 <- fields::cover.design(scale_expos, nd = 100)$design
Error in fields::cover.design(scale_expos, nd = 100) :
Error: R must not have duplicate rows