u/Exact_Yak7780

I have 2 cats. One is 6 and other 3. The female 6 year old is pooping outside the box. There is nothing wrong with her except she tolerates other cat but isn’t particularly friendly to him. I just ordered a stainless box. I already have 2 boxes. Any advice? I’m also trying new litter. This problem is 6 months d now.