An Azure service that enables developers and testers to generate insights on how to improve the performance, scalability, and capacity usage of their application
In Azure Load Testing, JMeter does not see your local file paths. ALT unpacks all uploaded files into the /jmeter/user-files directory. So any path coming from your CSV must be relative to that folder.
Fix:
Upload your CSV and JSON files to ALT in the same upload bundle as the JMX.
In your CSV, keep only the file name, not a full or local path. Example: payload1.json
In your sampler, read it like this: ${__FileToString(/jmeter/user-files/${ERequestBody},,)}
You do not need __eval in ALT.
I think this works because ALT resolves files only from /jmeter/user-files. Let me know how this worked.
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