AWS GO SDK returns "AuthFailure: AWS was not able to validate the provided access credentials"

Question

I am developing a simple automation tool using a Go Fiber HTTP server to start and stop AWS instances using the Go SDK v1.44.156.

The service listens to an endpoint at /csm/aws/:region/:instance_id/powerOn.

My code works well when I send requests from Postman. When I send requests using the Go HTTP client, AWS returns the following error:

AuthFailure: AWS was not able to validate the provided access credentials

The Postman request that works fine:

2022/12/23 16:26:12 Request came :#0000000100000003 - 127.0.0.1:7000 <-> 127.0.0.1:34976 - POST http://127.0.0.1:7000/csm/aws/us-east-1/i-0f9c5fe6b5c7b0a87/powerOn
Params: map[instance_id:i-0f9c5fe6b5c7b0a87 region:us-east-1]
Request: POST /csm/aws/us-east-1/i-0f9c5fe6b5c7b0a87/powerOn HTTP/1.1
User-Agent: PostmanRuntime/7.30.0
Host: 127.0.0.1:7000
Content-Type: application/json
Content-Length: 136
Accept: */*
Postman-Token: e27b899f-5125-497a-b154-61cd3214cd74
Accept-Encoding: gzip, deflate, br
Connection: keep-alive

{"aws_access_key_id":"my-id","aws_secret_access_key":"my-key","account":"","region":""}

The Go request which returns the error:

2022/12/23 16:22:02 Request came :#0000000200000002 - 127.0.0.1:7000 <-> 127.0.0.1:34278 - POST http://127.0.0.1:7000/csm/aws/us-east-1/i-0f9c5fe6b5c7b0a87/powerOn
Params: map[instance_id:i-0f9c5fe6b5c7b0a87 region:us-east-1]
Request: POST /csm/aws/us-east-1/i-0f9c5fe6b5c7b0a87/powerOn HTTP/1.1
User-Agent: Go-http-client/1.1
Host: 127.0.0.1:7000
Content-Type: application/json
Content-Length: 136
Accept-Encoding: gzip

{"aws_access_key_id":"my-id","aws_secret_access_key":"my-key","account":"","region":""}

I searched on the web and I found information about this error message. It seems like it can be due to the time of the PC so I set my computer's time to automatic, but I see the same error.

My code was working a few days ago.