API Gateway - Execution failed: Resource forbidden due to invalid API Key

API gateway is returning:

< HTTP/2 403 
< date: Sun, 07 Jul 2024 02:51:24 GMT
< content-type: application/json
< content-length: 24
< x-amzn-requestid:
< x-amzn-errortype: BadRequestException
< x-amz-apigw-id:=
< 
* Connection #0 to host example.execute-api.ap-southeast-2.amazonaws.com left intact
{"message": "Forbidden"}%

when api key required is configured for a method.

In CloudWatch logs a single entry that says "Execution failed: Resource forbidden due to invalid API Key"

Things that have been checked in the web console:

• key added to a usage plan
• usage plan assigned to stage
• api key is correct
• request is being sent with "X-Api-Key"
• key is correct
• stage is deployed
• method is correct
• no other authroizer enabled