For COD dropshipping stores, how bad is your RTO rate?

Developer here, trying to understand the real economics of COD for dropshipping stores.

If you offer COD, what % of your orders end up as RTO/failed deliveries, and what does one failed order cost you after shipping, return shipping, product handling, etc.?

Do you use anything to verify COD orders before shipping — IVR, WhatsApp, OTP, confirmation calls, etc.? Has it actually reduced RTO?

And has anyone tried charging a small COD fee or taking a partial advance to filter low-intent orders? Did it reduce RTO, and if so, did you notice any impact on conversion?

Full disclosure: I'm building a small tool in this space, so I have skin in the game. Deliberately not naming or linking it, this post is to learn, not to sell.

I'll compile whatever gets shared and post the aggregate back here for everyone.