Power Automate HTTP Request POST ends with "Internal Server Error" - httprequest

Question

I'm not sure why I face an "Internal Server Error" when I send an POST Request with Power Automate, but if I send the same request with Postman it works just fine. As you can see the flow tried 4 times until it stopped. I call the same REST API with Postman and it works without problems. The Authorization is by the way Basic with Username and Password.
This is the response from Postman when I send the POST request:
{
"executionTime": 3360,
"hints": [
{
"id": "STRING",
"name": "STRING",
"type": "GROUP_HINT",
"locations": [
{
"tokens": [
{
"start": 33,
"end": 41
},
{
"start": 61,
"end": 66
}
],
"score": 1.0,
"distance": 0,
"groupValue": {
"left": "STRING",
"right": "STRING"
}
}
],
"groupElement": [
"MATCHED GROUPS"
],
"range": 20
}
],
"businessCases": [
{
"businessCaseId": "ee05f8f9-e18d-4bf7-b7db-4c8bc800615a",
"name": "STRING",
"score": 0.53,
"hintCount": 1596,
"originCount": 241,
"matchedHints": [
"MATCHED GROUPS"
],
"matchedBoostedHints": [
"MATCHED GROUPS"
],
"origins": [],
"matchedOrigins": [
"MATCHED GROUPS"
],
"matchedBoostedOrigins": [
"MATCHED GROUPS"
],
"unmatchedOrigins": []
}
],
"questions": [],
"extractedValues": []
}
The REST API should analyse the text in the POST request and return any matched groups through sentiment analysis.