Creates a session URL for the authenticated user to manage their Stripe subscription via the customer portal.
curl --request POST \
--url https://api.fluxer.app/v1/premium/customer-portal \
--header 'Authorization: <api-key>'{
"url": "<string>"
}curl --request POST \
--url https://api.fluxer.app/v1/premium/customer-portal \
--header 'Authorization: <api-key>'{
"url": "<string>"
}