What do I answer?

What do you say to an ex after she reached out to you after a long time?

We were together for like 2 years, we had ups and downs but it ended.

I met someone new and and I'm really happy with her.

After a time the ex reached out to ask how i'm doin.

We exchanged like 4 texts, I told her I met someone new and the answer was in style: ,,I'm happy for you, i wont make it difficult and this is last message from me, have a good life".

I dont know what to say to this.

Should I answer?  I feel like she deserves and answer but if I say something like: ,,Thank you, you too." That sounds weird and stupid but I dont know what to say.

Thank you