Call to undefined method Symfony\Component\Mime\Header\Headers::addHeader()

Hi,

I'm having the same problem, but only when i'm logged in Drupal via SimpleSAML. I installed everything via composer. Did you find solution for this @La558 ? Thx.

Regards.

Found another way this error can occur, on a D9 / CiviCRM site with the Omnipay CiviCRM extension, which includes an older copy of the Symfony mime library. Details at symfony conflicts with D9.

Hey @davej,

You wrote: "The version of mime in the extension (4.4.0) lacks the addHeader() method in Headers.php, however it's present in the D9 version of mime (5.2.0 in this case)." in that post, but i don't understand which extension you talk about - webforms? I can not find "mime" extension in D9 so how do you upgrade mime to higher version? Thx.

Regards.

This is really strange. So, the mime version i'm using in vendor/symfony/mime/ is 5.2 and in file:

vendor/symfony/mime/Header/Headers.php

there is a function called addHeader but i still get this error. What is going on here??

Hi @orcalator, most likely there are multiple copies of the Mime library and the code is picking up an older one that doesn't have the addHeader() method. #16 had this issue with Simplesamlphp.