Extensions not accessing composer vendor functions

[valzargaming]

I have checked \vendor\guzzlehttp\guzzle\src\Util.php and verified that the method does indeed exist.

[08282aca7c36d813ecff7482] /index.php?title=Special:OAuth2Client/redirect Error: Call to undefined method GuzzleHttp\Utils::chooseHandler()

Backtrace:

from C:\WinNMP2021\WWW\bcwiki\vendor\guzzlehttp\guzzle\src\functions.php(61)
#0 C:\WinNMP2021\WWW\bcwiki\extensions\MW-OAuth2Client\vendors\oauth2-client\vendor\guzzlehttp\guzzle\src\HandlerStack.php(42): GuzzleHttp\choose_handler()
#1 C:\WinNMP2021\WWW\bcwiki\extensions\MW-OAuth2Client\vendors\oauth2-client\vendor\guzzlehttp\guzzle\src\Client.php(65): GuzzleHttp\HandlerStack::create()
#2 C:\WinNMP2021\WWW\bcwiki\extensions\MW-OAuth2Client\vendors\oauth2-client\src\Provider\AbstractProvider.php(131): GuzzleHttp\Client->__construct(array)
#3 C:\WinNMP2021\WWW\bcwiki\extensions\MW-OAuth2Client\vendors\oauth2-client\src\Provider\GenericProvider.php(99): League\OAuth2\Client\Provider\AbstractProvider->__construct(array, array)
#4 C:\WinNMP2021\WWW\bcwiki\extensions\MW-OAuth2Client\SpecialOAuth2Client.php(54): League\OAuth2\Client\Provider\GenericProvider->__construct(array)
#5 C:\WinNMP2021\WWW\bcwiki\vendor\wikimedia\object-factory\src\ObjectFactory\ObjectFactory.php(244): SpecialOAuth2Client->__construct()
#6 C:\WinNMP2021\WWW\bcwiki\vendor\wikimedia\object-factory\src\ObjectFactory\ObjectFactory.php(150): Wikimedia\ObjectFactory\ObjectFactory::getObjectFromSpec(array, array)
#7 C:\WinNMP2021\WWW\bcwiki\includes\specialpage\SpecialPageFactory.php(1218): Wikimedia\ObjectFactory\ObjectFactory->createObject(string, array)
#8 C:\WinNMP2021\WWW\bcwiki\includes\MediaWiki.php(273): MediaWiki\SpecialPage\SpecialPageFactory->getPage(string)
#9 C:\WinNMP2021\WWW\bcwiki\includes\MediaWiki.php(930): MediaWiki->performRequest()
#10 C:\WinNMP2021\WWW\bcwiki\includes\MediaWiki.php(564): MediaWiki->main()
#11 C:\WinNMP2021\WWW\bcwiki\index.php(53): MediaWiki->run()
#12 C:\WinNMP2021\WWW\bcwiki\index.php(46): wfIndexMain()
#13 {main}