Is there a way in php to check if a standalone account connected to your stripe application is verified (meaning that a user has confirmed his identity uploading an id document approved by stripe)?
Simply retrieve the account:
$account = \Stripe\Account::retrieve("acct_...");
You can then check the following boolean attributes:
$account->details_submitted: Whether or not account details have been submitted yet. Standalone accounts cannot receive transfers before this is true.
$account->charges_enabled: Whether or not the account can create live charges
$account->transfers_enabled: Whether or not Stripe will send automatic transfers for this account. This is only false when Stripe is waiting for additional information from the account holder.
(Source: description of the account object.)