how to enable route propagation in the routing tables

its 3 year old question but no updates have been done to suggest if you were able to solve it or not. If solved what was the problem. I feel it to be a Transit Gateway Route Table Association/Propagation not setup or missing. Make sure each VPC attachment Is associated with a TGW route table and Has route propagation enabled. Less likely condition but possible that IAM Permissions for TGW Propagation are missing. Other issue can be that Route Tables in VPCs Not Sending data to TGW. Some propagations fail because Terraform doesn't wait for the attachment to fully complete before enabling propagation. Use depends_on explicitly.