Webhook URL validation failed randomly after working for months

we have a user-manages oauth app that receives webhooks. It was working for months and suddenly the url validation fails. the endpoint is an aws node lambda function. I have checked the domain mapping, domain health, and certificate everything is good. post requests also work on postman. I have tried regenerating the secret token but no luck. Please advise webhook functionality is essential to our app. Here is the relevant bit of code from the lambda function.

if (request.event === 'endpoint.url_validation') {
            const hashForValidate = crypto.createHmac('sha256', zoomWebhookSecretToken)
                .update(request.payload.plainToken)
                .digest('hex');

            const responseBody = {
                plainToken: request.payload.plainToken,
                encryptedToken: hashForValidate
            };
            console.log('responseBody:', responseBody )
            return {
                statusCode: 200,
                headers: {
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify(responseBody)
            };
        }

It sounds like there might be changes in the server configuration or the webhook’s endpoint. Check for any recent updates or modifications on both ends, and review the validation process to troubleshoot the issue.