After Sending Email error Massage

After sending invoices or quotes I get the following error message.

PHP Error was encountered

Severity: 8192

Message: Array and string offset access syntax with curly braces is deprecated

Filename: src/Mpdf.php


File: /home/vendor/composer/ClassLoader.php
Line: 444
Function: _error_handler

File: /home/vendor/composer/ClassLoader.php
Line: 444
Function: include

File: /home/vendor/composer/ClassLoader.php
Line: 322
Function: Composer\Autoload\includeFile

File: /home/application/helpers/mpdf_helper.php
Line: 49
Function: spl_autoload_call

File: /home/application/helpers/pdf_helper.php
Line: 259
Function: pdf_create

File: /home/application/helpers/mailer_helper.php
Line: 110
Function: generate_quote_pdf

File: /home/application/modules/mailer/controllers/Mailer.php
Line: 212
Function: email_quote

File: /home/index.php
Line: 325
Function: require_once

what could this be I have updated my servers to PHP 7.4

Hi, what InvoicePlane version are you on? (I also have instances running on PHP7.4 and do not have the error). Here you can find the last version on InvoicePlane which does support PHP7.4 InvoicePlane - Downloads - InvoicePlane - An Open Source Invoicing Application

IP 1.5.11 think its got something to do with the PDF as I can not view or download the PDFs

Ok After looking at this closely I have noticed that IP 1.5.11 can only run on PHP 7.3 without any errors, if I update to PHP 7.4 I get a long list of errors listed above. but when I update to PHP 8 I get one error but the error does not make sense and the whole IP is down. error is application/third_party/MX/Modules.php line 84 each()

“Call to undefined function each()”

// @TODO @each will suppress errors but needs to be replaced if the function is removed in PHP 7.3
is_array($module) ? list($module, $params) = @each($module) : $params = NULL;

so I switch back to 7.3 not that I wanted to but because I had to