Route specific @ adresses from Google suite to OVH

Hi there,
I am trying to build a setup where some of my addresses are handled by Google Suite, and some other are handled by OVH.
I have managed to have regular emails on Google Suite (`john.doe@example.org`). Now I want to add specific @ addresses to OVH (`foo.bar@example.org`).

I have understand that it is possible to do such thing on GG Suite by using Routing and using `split delivery` : https://support.google.com/a/answer/2685650?hl=en&ref_topic=2921034

I have followed the steps in the docs. Now, on OVH webadmin, I have created a standard email account for foo.bar and I managed to add it to my email client (thunderbird). I can successfully send emails from foo.bar.

The issue is reception. When I try to send a message to foo.bar, I receive the following error :
Message not delivered
There was a problem delivering your message to `foo.bar@example.org`. See the technical details below, or try resending in a few minutes.
The response from the remote server was:

530 5.7.1 Client was not authenticated

Reporting-MTA: dns; googlemail.com
Received-From-MTA: dns; mysender@example.org
Arrival-Date: Mon, 11 Feb 2019 01:56:33 -0800 (PST)
X-Original-Message-ID:

Final-Recipient: rfc822; foo.bar@example.org
Action: failed
Status: 5.7.1
Remote-MTA: dns; ssl0.ovh.net (193.70.18.144, the relay for the domain.)
Diagnostic-Code: smtp; 530 5.7.1 Client was not authenticated
Last-Attempt-Date: Mon, 11 Feb 2019 01:56:34 -0800 (PST)


Any idea ?