Lambda Function Serverless permission - amazon-web-services

Question

I've been developing an aws lambda function with python and serverless. It reads files from a s3 bucket and stores data from it in another bucket as a csv. The code works perfectly with invoke local but after deploying I get:
An error occurred (AccessDenied) when calling the PutObject operation: Access Denied
This is the function:
s3_client.put_object(Body=data, Bucket=bucket_name, Key=key_name)
and part of the serverless yml
iamRoleStatements:
- Effect: Allow
Action:
- KMS:Decrypt
Resource: '*'
- Effect: Allow
Action:
- 's3:*'
Resource:
- 'arn:aws:s3:::output_bucket'
- 'arn:aws:s3:::output_bucket/*'
- Effect: Allow
Action:
- 's3:ListBucket'
Resource:
- 'arn:aws:s3:::input_bucket'
- 'arn:aws:s3:::input_bucket/*'
- Effect: Allow
Action:
- 's3:GetObject'
Resource:
- 'arn:aws:s3:::input_bucket'
- 'arn:aws:s3:::input_bucket/*'
Is there any other configuration I need? Am I missing something obvious?

Answer 1

For me the indent looks wrong. Please make sure to use it right.
iamRoleStatements:
- Effect: Allow
Action:
- 'kms:Decrypt'
Resource: '*'
- Effect: Allow
Action:
- 's3:*'
Resource:
- 'arn:aws:s3:::output_bucket'
- 'arn:aws:s3:::output_bucket/*'
- Effect: Allow
Action:
- 's3:ListBucket'
- 's3:GetObject'
Resource:
- 'arn:aws:s3:::input_bucket'
- 'arn:aws:s3:::input_bucket/*'
FYI: I merged s3:ListBucket and s3:GetObject into one statement.