Token Holdings and Balance
There are a couple of requests you can use to check the balance of a given token for a given account or you can check if an account has a number of different tokens.
Remember, for a given call to check the account holdings or an individual balance you need to be aware whether an account ID is valid for a given environment. As an example, the amount of accounts on testnet far exceeds that of mainnet, thus you may receive errors if you try to pass an incorrect accounts into different environments.
This returns back to Balance for a given token that belongs to a given account, you can use this as an alternative to balance lookups on mirror nodes, if balance requests are critical.
Get Token Balance
Perhaps you just want to know whether an account holds particular tokens, this could be helpful if you are a building service that requires one or many tokens (like NFTs) to be held to unlock access to particular feature of your service.
Get Account Holdings