Request failed with status code 400 for Relay at Polygon mainnet but works at Mumbai

I have 2 similar Relayers: one for Mumbai testnet and another one for Polygon mainnet. I'm using Relay to publish contracts. The code is basically the same as here: It works perfectly for Mumbai but I keep getting "Request failed with status code 400" when I try to use mainnet. I've tried to re-create API keys and Relay itself - still the same.