error in step3 preview: Class "TijsVerkoyen\CssToInlineStyles\CssToInlineStyles" not found

[Frank]

TYPO3: 11.5.29 (classic installation - no composer!)
luxletter: 21.0.0

everything works fine, until step3, where i get the error:
503
Oops, an error occurred!
Class "TijsVerkoyen\CssToInlineStyles\CssToInlineStyles" not found

also the cronjob did not work and shows the same message

How can i implement the package from https://github.com/tijsverkoyen/CssToInlineStyles
or is there a way to deactivate the CssToInlineStyles-process ?

thanks

[Alexander Kellner]

This sounds to me that you didn't install LUXletter via composer as it is requested in the documentation?

[Frank]

yes, i don't have shell access to our clients server and therefore none composer

[Alexander Kellner]

Thx for the final feedback. This is not a failure but more an installation issue.