Solution:
If you must append multiple secrets to a URL like you are saying you can save the entire portion of the URL as a single secret. Instead of saving key0 and key1 as individual secrets it would be something like setting a secret as: ?key={your-key-here}&token={your-token-here} for the domain you want to use. Not the cleanest solution, but it should fix your problem.
Security Concern:
If possible you should really be passing these arguments as headers rather than as part of the URL. While I don’t think you will have any security problems with Roblox’s servers making these calls, it’s best practice to do this and is good to build as a habit. If the API you are using doesnt support that then ¯\(ツ)/¯ but if it’s your own API I suggest implementing authentication checks via headers and not just URL queries.
I’d like to see compatibility with being able to pass both secrets and stringswith AddSuffix and AddPrefix, but currently we can only pass strings as an argument for these methods. Having multiple keys as a query rather than passed headers is something that a lot of legacy APIs use and it could be nice to have some support for the older web.