We use Web service data source in a report which has long OData query. 
After adding filters, the OData query becomes too long. That's why it causes 404.15 error.

This is probably due to the limitation of maximum Url length in browsers. It is about 2048 characters (for IE). So there different limits for different browsers and web servers. https://www.geeksforgeeks.org/maximum-length-of-a-url-in-different-browsers/

To solve the issue probably we can use POST method in the web service data source instead of GET method. 

I have  "@url", "$select", "$expand" and "$filter" parameters set in the data source. How to use those parameters in body of the post request? And is it good solution?

As a sample report you can use attached report (TestProductReport.zip). The sample report has web service data source. The query in Service URL is short in this case, but we have long query in other report.

Getting error 400 when previewing the sample report. Any idea to fix this issue?

Hi,

I'm struggling to authenticate a Microsoft Dynamics 365 webservice with OAuth2.

I'm using the Web Service Data Source wizard within the Report designer to connect to the Web service but not having any luck. I can successfully access the Web service and OAuth2 API in Postman. 

When I try to download the response in the preview window, I get a 400 bad request error. I believe the problem is with fetching the token/authentication but not sure.

Can someone please tell me what I'm doing wrong?