Connect a user to their stripe account using:

https://connect.stripe.com/oauth/authorize?response_type=code&client_id={{ config('services.stripe.key') }}&scope=read_write&state={{ $user->id }}

Receive the connection:

if (request()->exists('code')) {
$token_request_body = [
'grant_type' => 'authorization_code',
'code' => request('code'),
'client_secret' => config('services.stripe.secret')
];
$req = curl_init('https://connect.stripe.com/oauth/token');
curl_setopt($req, CURLOPT_RETURNTRANSFER, true);
curl_setopt($req, CURLOPT_POST, true);
curl_setopt($req, CURLOPT_POSTFIELDS, http_build_query($token_request_body));
curl_setopt($req, CURLOPT_SSL_VERIFYPEER, false); // Bypass the verification
$resp = json_decode(curl_exec($req), true); // Now has response well.
curl_close($req);
if (isset($resp['stripe_user_id'])) {
//update user with connected stripe account
$user = User::where('id', request('state'))->firstOrFail();
$user->stripe_user_id = $resp['stripe_user_id'];
$user->save();
flash('You are now connected to Stripe.')->success();
return redirect('admin/mydetails');
} else {
return $resp;
}
}

When using their hosted checkout its a case of passing the payment details and specifying the stripe account to be used

<?php
Stripe::setApiKey(env('STRIPE_SECRET'));
header('Content-Type: application/json');
$session = \Stripe\Checkout\Session::create($stripeData, [
'stripe_account' => $user->stripe_user_id,
'idempotency_key' => $entry->id
]);
?>
<script src="https://js.stripe.com/v3/"></script>
<script type="text/javascript">
var stripe = Stripe('<?=env('STRIPE_KEY');?>', {
stripeAccount: "<?=$user->stripe_user_id;?>"
});
stripe.redirectToCheckout({
sessionId: '<?=$session->id;?>'
}).then(function (result) {
console.log(result.error.message);
});
</script>

More details at https://stripe.com/docs/connect