Getting "internal server error" on passing binary data to AWS Lambda function deployed using serverless framework and apigw-binary plugin - aws-lambda

Question

what I'm trying
Passing binary data via Lambda integration in API gateway. Lambda returns back text.
issue
The function returns desired output when API gateway is configured from console. To implement it using serverless framework I installed serverless-apigw-binary plugin. The required binary types show up in API gateway>settings>binary media types. However on calling API I get "internal server error". The function works properly on application/json type input. After enabling-disabling lambda proxy integration and adding mappings via console, I get correct output.
serverless.yml file
org: ------
app: ---------
service: ---------
frameworkVersion: ">=1.34.0 <2.0.0"
plugins:
- serverless-python-requirements
- serverless-offline
- serverless-apigw-binary
provider:
name: aws
runtime: python3.7 #fixed with pipenv
region: us-east-1
memorySize: 128
timeout: 60
profile: ----
custom:
pythonRequirements:
usePipenv: true
useDownloadCache: true
useStaticCache: true
apigwBinary:
types: #list of mime-types
- 'application/octet-stream'
- 'application/zip'
functions:
main:
handler: handler.main
events:
- http:
path: ocr
method: post
integration: lambda
request:
passThrough: WHEN_NO_TEMPLATES
template:
application/zip: '
{
"type": "zip",
"zip": "$input.body",
"lang": "$input.params(''lang'')",
"config": "$input.params(''config'')",
"output_type": "$input.params(''output_type'')"
}'
application/json: '
{
"type": "json",
"image": $input.json(''$.image''),
"lang": "$input.params(''lang'')",
"config": "$input.params(''config'')",
"output_type": "$input.params(''output_type'')"
}'
application/octet-stream: '
{
"type": "img_file",
"image": "$input.body",
"lang": "$input.params(''lang'')",
"config": "$input.params(''config'')",
"output_type": "$input.params(''output_type'')"
}'
handler.py
def main(event, context):
# do something on event and get txt
return txt
edit
I compared swagger definitions and found this
1. API generated from console(working)
paths:
/ocr:
post:
consumes:
- "application/octet-stream"
produces:
- "application/json"
responses:
API generated from serverless framework
paths:
/ocr:
post:
consumes:
- "application/x-www-form-urlencoded"
- "application/zip"
- "application/octet-stream"
- "application/json"
responses:
produces: - "application/json" is missing. How do I add it in serverless?