The casino verification process is a regulatory requirement before it is a customer-service problem. An operator has to know who holds an account, that the person is old enough, that they are where they say they are, and — beyond certain thresholds — where the money came from. Those are four different obligations and they are satisfied by different documents.
Identity
A government-issued photo document, matched to the name on the account. The common failure is a mismatch: a shortened first name, a married surname, or an account opened in one spelling and a document in another.
Address
Something recent, in your name, showing the address on the account — typically a utility bill or a bank statement. Screenshots of online banking are often refused; a downloaded PDF statement usually is not.
Source of funds
Triggered by amount or by pattern rather than by suspicion of the individual, and read by a person rather than by a system. This is the check that adds days, and the only one that can reasonably ask for payslips, a tax document or a transaction history.
When it happens, and why that is the problem
Almost always at withdrawal rather than at deposit. An account can pay in for months untouched and then face all three checks at the moment money is requested back — which is why an "instant" withdrawal usually isn't one. Clearing identity and address before you ever request a payout removes most of that delay; source of funds cannot be pre-cleared, but knowing the threshold tells you when to expect it.
Who sees the documents, and for how long
Usually a payments or compliance team rather than customer support, which is why the person answering a chat window often cannot say more than that it is with the department. Documents are normally retained for a statutory period after an account closes, and that retention is why a re-opened account sometimes needs nothing while a new one at the same operator needs everything again.
What the operator is obliged to establish
That the account holder is who they say they are, that they are old enough, that they are in a jurisdiction the licence covers, and — beyond defined amounts — that the money has a plausible origin. Those obligations sit with the operator whatever payment method a player used, which is why switching methods never shortens the check.
The one thing that reliably speeds it up
Consistency. The name on the account, the name on the document and the name on the bank account should be identical, and the address should match on all three. Almost every rejection is a mismatch of that kind rather than a judgement about the person.
Frequently asked
When will I be asked to verify?
Almost always at withdrawal rather than at deposit, which is why a first payout so often stalls.
Can I verify before I withdraw?
Identity and address can usually be cleared as soon as an account is open. Source of funds cannot be pre-cleared.
Why was a screenshot of my online banking refused?
Most operators require a document rather than a screen capture; a downloaded PDF statement is normally accepted.
Does a bigger withdrawal face more checks?
Yes. Thresholds trigger additional review, and above them a human reads the file rather than a system.