Metis Explorers support `@openzeppelin/hardhat-upgrades` plugin now

openzeppelin-hardhat-upgrade-support.md

Deploy

$ npx hardhat run --network metisGoerli scripts/deploy.ts                            
No need to generate any newer typings.
upgradeable contract deployed to address: 0xa15f9245d1E8c25598dE2605871A2b5854371cF2

Verify

npx hardhat verify --network metisGoerli 0xa15f9245d1E8c25598dE2605871A2b5854371cF2
Verifying implementation: 0x94222444b8F6a9Df48671e80EB234E5C5852b5EB
Nothing to compile
No need to generate any newer typings.
Successfully submitted source code for contract
contracts/VastToken.sol:VastToken at 0x94222444b8F6a9Df48671e80EB234E5C5852b5EB
for verification on the block explorer. Waiting for verification result...

Successfully verified contract VastToken on Etherscan.
https://goerli.explorer.metisdevops.link/address/0x94222444b8F6a9Df48671e80EB234E5C5852b5EB#code
Verifying proxy: 0xa15f9245d1E8c25598dE2605871A2b5854371cF2
Successfully verified contract ERC1967Proxy at 0xa15f9245d1E8c25598dE2605871A2b5854371cF2.
Linking proxy 0xa15f9245d1E8c25598dE2605871A2b5854371cF2 with implementation
An unexpected error occurred:

Error: Etherscan API call failed with status 400, response: {"message":"Unknown action","result":null,"status":"0"}

you can still see an error, the reason for the error is an api we don't support, but it doesn't matter, you can just ignore the error.

the feature has been online on our Andromeda and Goerli both.

Happy building on Metis!