Financial Services Verification is necessary?

I think If you’ve completed every step and still get rejected then contact Google Ads support with the verification approval and disapproval details because It could be an account-level mismatch.

Yes, google has different financial services requirements depending on the country and type of service. you should check whether your client's specific service needs additional approval.

Google's new policy has become stricter, it requires two types of verification, one is advertiser verification and the other is financial services verification. I think you should check whether all the details of the business are in accordance with Google's policy or not. Also make sure that the account is being verified through the same domain that is being verified. If everything is correct, contact Google Ads support and find out the real reason for the rejection, usually this problem is resolved in two to three days.

You should check the G2RS requirements as well if your target country requires it because just completing google's advertiser verification alone may not be enough.