Help with Amazon PA-API v5 - Getting InternalFailure (404) despite active keys

[leoalmeida007]

Body:
Hi everyone,

I'm trying to use the Amazon Product Advertising API v5 (PAAPI) to fetch product data from amazon.com.br using my affiliate credentials.
My keys are active, and my account has already generated commissions.

However, every time I make a request, I get the following error:

json
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{
"codigo_http": 404,
"erro_curl": "",
"resposta_bruta": {
"Output": {
"__type": "com.amazon.coral.service#InternalFailure"
},
"Version": "1.0"
}
}
Request Details:
Region: us-east-1

Host: webservices.amazon.com.br

Marketplace: www.amazon.com.br

URI path: /paapi5/searchitems

HTTP Method: POST

PHP with curl

Target: com.amazon.paapi5.v1.ProductAdvertisingAPIv1.SearchItems

Authorization headers and signature are generated using AWS Signature v4.
Here’s a shortened version of my payload:

json
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{
"Keywords": "notebook",
"ItemCount": 3,
"Resources": [
"Images.Primary.Medium",
"ItemInfo.Title",
"Offers.Listings.Price"
],
"PartnerTag": "mixbr0d-20",
"PartnerType": "Associates",
"Marketplace": "www.amazon.com.br"
}
I’ve followed all guidelines on:

API documentation

Signing AWS Requests

I've confirmed with Amazon Associates support that my keys are active, but they couldn’t provide technical assistance.

Has anyone experienced something similar or sees what might be wrong here?

Thanks in advance!