Thank you for reaching out.
If I have understood correctly, the JSON request body in your web request is getting blocked by your WAF. You tried adding the
Request body post args name exclusion rule but it did not work.
I think you should be able to exclude above JSON request body by adding a
Request body JSON args name instead. You can follow this documentation here to try and add this exclusion rule,
Hope this helps! Please do let me know if this exclusion rule does not work in your case. Thank you!