PHP code:
Checker: https://phpcodechecker.com
About failures: https://kinsta.com/blog/10-things-not-to-do-in-php-7

QR-code (Quick Response code):
– Online SEPA Credit Transfer QR-code generator: https://epc-qr.eu/?form
– Eg in PHP: $QRcode = “BCD\n002\n1\nSCT\n”.$BankBIC.”\n”.mb_substr($BankAccountHolder, 0, 70).”\n”.$BankIBAN.”\nEUR”.strval($ARAmount). “\n\n\n”.mb_substr($PaymentReference.” “.$InvoiceName.” (“.$InvoiceMember.”)”, 0, 140);

Site to find many programmers tools:
https://extendsclass.com/

Variable-width encoding:
Cutting a string value using substr() can crash inside a character of several bytes. Functions named like mb_substr() can handle a character of several bytes.
Note: ‘Multibyte character set’ is not a proper name for in fact multibyte encoding.

MariaDB database:
This MySQL database does not cut off longer values anymore. Using a state-of-the-art version, your application can raise bugs.

HTML using F12:
Statements get outdated in a process of depreciation. My suggestion is to warn your application supplier in order to fix before a warning in yellow becomes an error in red.