Mail script only working manually

I use the Mailscript “Add attachement to Devonthink” to automatically send pdfs in incoming mails to Devonthink. It works perfectly fine if I do it manually after new mails came in, but it is not working automatically. For testing I put additional actions in the rule and these work automaticially. Only the transfer of the pdf won´t work.

Any ideas to solve this problem? Or an idea for a different workflow? Thank you very much!