Rest API connector working in Postman but not in Power Automate

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Posted on by forstera

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Hello all,

I've a connector which is working when I'm testing it in postman or other test tools but not with Power Automate.

I need to make a POST to the following address :

https://mese.webuntis.com/WebUntis/jsonrpc.do?school=gym_Biel-Bienne

Here, it works fine and I get a Session ID :

But when I do the same in Power Automate it doesnt work :

Result :

Could it be a certificate problem ?

Thanks to all for your help 🙂

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Using connectors

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lbendlin 8,474 Super User 2025 Season 2 on at

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Likely you need to explicitly specify the expected content type.

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forstera 331 on at

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Hello @lbendlin and sorry .. yes of course I forgott that, sorry.

So, I work for a school and I need to authenticate to that application to retrieve timetables teachers and students.

The authentication process should be like this :
{"id":"ID","method":"authenticate","params":{"user":"ANDROID", "password":"PASSWORD", "client":"CLIENT"},"jsonrpc":"2.0"} The parameter CLIENT is a unique identifier for the client app. The parameter client will be mandatory in the future. result: {"jsonrpc":"2.0","id":"ID","result": {"sessionId":"644AFBF2C1B592B68C6B04938BD26965","personType"=2,"personId"=17}
When I try to authenticate using, from example, postman or another tool I found in the web it wors with the following data :
When posting with them, I receive the following answer :
Then I can use the "SessionID" to make my request.

But now, when I do the same using the html component of Power Automate, the answer is not the same and I dont receive any SessionID:

Here's my html component to post :
and here's the answer : we can see that it's completely different that the one here above and the one expected which should be :
{"jsonrpc":"2.0", "id":"ID", "result": {"sessionId":"644AFBF2C1B592B68C6B04938BD26965", "personType"=2, "personId"=17}

So I dont know howto define my html component to make it working ...
Thanks to all for your help 🙂

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lbendlin 8,474 Super User 2025 Season 2 on at

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Great, you get stuff back. Your content is Base64 encoded. Decode it and then use that.

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forstera 331 on at

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so, do you mean that if I take the following answer

{ "statusCode": 200, "headers": { "Connection": "keep-alive", "requestId": "39beb5ff218dd1ae054d4634595bd368", "Access-Control-Allow-Headers": "Accept, Origin, X-Requested-With, Content-Type, Last-Modified", "Access-Control-Allow-Origin": "*", "Date": "Tue, 20 Jun 2023 12:51:33 GMT", "Server": "nginx", "Content-Length": "84" }, "body": { "$content-type": "application/octet-stream", "$content": "eyJqc29ucnBjIjoiMi4wIiwiaWQiOiJlcnJvciIsImVycm9yIjp7Im1lc3NhZ2UiOiJpbnZhbGlkIHNjaG9vbG5hbWUiLCJjb2RlIjotODUwMH19" } }
and I convert it to base64
base64ToString(MyAnswer)
I'll get something like this ?

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lbendlin 8,474 Super User 2025 Season 2 on at

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When you use Base64decode on this

eyJqc29ucnBjIjoiMi4wIiwiaWQiOiJlcnJvciIsImVycm9yIjp7Im1lc3NhZ2UiOiJpbnZhbGlkIHNjaG9vbG5hbWUiLCJjb2RlIjotODUwMH19

you get

{"jsonrpc":"2.0","id":"error","error":{"message":"invalid schoolname","code":-8500}}

🙂

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forstera 331 on at

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ah ok, thanks very much I understand the meaning yet.

What is really strange to me is when sending informations via another tool (postman for example) it works. I just copied and pasted into the Power Automate html component. Do you think I should convert it before sending, too ?

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Verified answer

lbendlin 8,474 Super User 2025 Season 2 on at

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Look at the Raw tabs in Postman, see what's really happening.

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forstera 331 on at

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Thanks very much for the informations, I'll have a look a learn about it 🙂

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