Give up trying. Mine are 18 months old now and still won’t sleep. Learn to operate on 3 hours sleep and weep often.
This. 19 month old little angel goes to her own bed fine, but always ends up in the big bed with her Mammy (no) around 3am-4am, which results in me finishing off my kip on a single mattress on the back bedroom floor. Just go with it, it won't be forever (probably).