Forwarding a forwarding via routing

[DriveMyBus]

Hello,

I have the following problem: an e-mail that has already been forwarded is to be forwarded again to a third mailbox. I am currently trying to do this via the routing: https://admin.google.com/ac/apps/gmail/routing and have found the following instructions: https://support.google.com/a/answer/6297084?hl=de?hl=de

The forwarding(s) work from mailbox 1 to mailbox 2 without any problems, then my routing should take effect and forward from mailbox 2 to mailbox 3 - which does not work.

If I send an e-mail to mailbox 2, the forwarding to mailbox 3 works without any problems.

Mailbox 1 (Company 1) -->> Mailbox 2 (Company 2) -->> Mailbox 3 (Company 3)

I must go this route due to contractual circumstances?

Who has a tip for me on how I can solve this?

Danke im voraus