Joomla 5: HTTP 500 / Compile Error: PG_Signature.php (line 17)

-- HikaShop version -- : 5.0.0
-- Joomla version -- : 5.0.0
-- PHP version -- : 8.2.11
-- Error-message(debug-mod must be tuned on) -- : HTTP 500

After upgrading to Joomla 5 and reinstalling Hikashop, in the configuration I received the message:
"Your PayPal payment method is obsolete and will soon be discontinued by PayPal. Please go in the System>Payment methods menu, click on the 'new' button..."

But when I click on NEW in the Payment Methods screen, it throws a 500 error:

Compile Error: Array and string offset access syntax with curly braces is no longer supported
/home/classica/public_html/plugins/hikashoppayment/platron/PG_Signature.php:17

Symfony\Component\ErrorHandler\Error\FatalError:
Compile Error: Array and string offset access syntax with curly braces is no longer supported

at /home/classica/public_html/plugins/hikashoppayment/platron/PG_Signature.php:17

Thanks. Yes, that fixed it.

NOTE:
This is one of my oldest HikaShop installs. Probably from 2012-13 or so.
It seems that "updates" to HikaShop are not removing all of the old code.