Blank Invoice screen/pop-up

-- HikaShop version -- : 4.7.1
-- Joomla version -- : 3.9.25
-- PHP version -- : 8.0
-- Browser(s) name and version -- : Firefox 110.0.1
-- Error-message(debug-mod must be tuned on) -- : Fatal error: Array and string offset access syntax with curly braces is no longer supported in /home/domains/vol4/916/2926916/user/htdocs/en/plugins/hikashop/attachinvoice/vendor/tecnickcom/tcpdf/tcpdf.php on line 16900

I get this error when I select an Order (edit) in the back-end and then click on the INVOICE button at the top. (Orders / Orders / click an order to edit). Without DEBUG on I just get a blank screen or pop-up
I get the same error if I select (tick) an order and click the INVOICE button on the main screen but full screen rather than a pop-up box

It was happening on an older HikaShop version but upgrading to the latest has not fixed the issue. It used to be fine on the old er version I was running until recently - so something has changed (a recent upgrade to PHP 8.0) to upset HikaShop.

If you need to log into the site I can supply a temp log-in for you.

Thanks

Thank you - but it won't install - the Joomla rotating busy symbol keeps going for hours and it never comes back or completes. I used
I uploaded the .zip file that downloaded from the email link that is in one of the purchase emails.

Pity there's not a discount for upgrading this plugin - I had to pay the full price to get the upgrade.

Thanks for any help on the Install issue.

Ignore last reply - it's finally done it. No idea why it was doing nothing but it finally worked on the 2nd attempt.

Invoices now download.

Thanks