AWS API Gateway and Lambda function deployed through terraform -- Execution failed due to configuration error: Invalid permissions on Lambda function

As per the suggestion from Denis Weerasiri, I checked the Lambda permissions after reselecting the Lambda function name in the Integration section of the API Gateway, and it had added another policy. The change that I needed to make was changing the v1 to a * in the source_arn in the Lambda function resource. So the new API Gateway trigger in my Lambda module looks like this:

resource "aws_lambda_permission" "post_session_trigger" {
     statement_id  = "Allow_My_Post_Session_Invoke"
     action        = "lambda:InvokeFunction"
     function_name = "${aws_lambda_function.init_function.function_name}"
     principal     = "apigateway.amazonaws.com"
     source_arn = "arn:aws:execute-api:us-east-1:${var.account_id}:${var.post_session_id}/*/POST/aa/ual/session"}