curl --location 'https://stg-gateway.invora.app/api/billing/v2/subscriptions/preview-proration' \
--header 'Content-Type: application/json' \
--data '{
"subscriptionId": "string",
"planId": "string"
}'{
"proratedAmount": {
"units": "string",
"nanos": 0
},
"currency": "CURRENCY_ENUM_UNSPECIFIED",
"effectiveAt": "2019-08-24T14:15:22.123Z",
"currentPlanId": "string",
"targetPlanId": "string"
}