Hi Damien,
I just recently connected to the Gmail channel and have it working to my expectations. But not without some issues along the way. If you have it figured out by now, you can ignore this, but maybe someone else will find it helpful.
My issue was with the Gmail Connector. Their help documentation didn't really spell it out clearly and I ended up starting a support case to get this resolved. During that process I requested that they update their help documentation, and they have.
Here's a link to STEP 4 of Gmail connector that may be useful:
https://helpv2.quickbase.com/hc/en-us/articles/9713253054484-Setting-up-a-Quickbase-Pipelines-Gmail-connector#:~:text=Step%204.%20Navigate%20to%20Manage%20Third%2DParty%20App%20Access
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Barry Dolan
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