AroundTheCorner

I am having a problem with a Redirect after a succesful payment in the Callback file. If I put a header("Location: $url") addInvoicePayment()- function, is ignored. If I put it in front, the redirect works just fine. I checked the addInvoicePayment and it returns true, so I assume there are no errors, only that there is no redirect. Anyone has a tip on how to debug/find a solution? if ($success) { addInvoicePayment($invoiceId,$transactionId,$paymentAmount,$paymentFee,$gatewayParams['name']); header("Location: ".$CONFIG['SystemURL']."/viewinvoice.php?id=$invoiceId&paymentsuccess=true"); exit(); } header location on top of addInvoice() works fine (I am aware the flow below makes no sense!). if ($success) { header("Location: ".$CONFIG['SystemURL']."/viewinvoice.php?id=$invoiceId&paymentsuccess=true"); exit(); addInvoicePayment($invoiceId,$transactionId,$paymentAmount,$paymentFee,$gatewayParams['name']); } Tested on Php7.4& Whmcs 8.2 Php 8.1 & whmcs 8.8 Thank you for any hints/suggestions.