Muttakin Islam Hasib

[remote oak]

You need to ensure you have available balance in your account for this

In test mode you can use our test cards that skip the pending balance delay, and you'll need to switch to manual payouts to accrue some positive balance of available funds

https://stripe.com/docs/testing#available-balance

[prime snow]

here is the balance in testmode

[remote oak]

Yes, that future payouts suggests you're using automatic payouts

funds are earmarked to be paid out and are not available to transfer in that case

Alternatively if this transfer follows a payment, you can use the source_transaction parameter to refer to a specific charge:
https://stripe.com/docs/connect/charges-transfers#transfer-availability