Monitoring API activity - Does AWS have a function that could help

Application and access logs can be monitored by outputting them to CloudWatch logs and setting up metrics filters.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/MonitoringLogData.html

For example, the API "/api/exemple" can be filtered and metrics such as number of accesses, number of failed executions, etc. can be set.

Another external monitoring is CloudWatch synthetics.
This allows the API to be periodically executed by CloudWatch and detected as an anomaly when it fails.
https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/CloudWatch_Synthetics_Canaries.html