Dear comunity, I ndd your help in order to find te error in my code because I've been trying to get the value of the two parameters of a weibull distibution (k and lamda)

nl(prevalence = ({k}/{lamda})*((dia_t2/{lamda})^({k}-1)*exp(-(dia_t2/{lamda})^{k})))

I have been modifying it but I always get the same message:

starting values invalid or some RHS variables have missing values

Could anybody help me to find where is the mistake?

Regards