I don't know if your specific configuration steps are correct. If you have installed the certificate correctly, when configuring the web service URL, you only need to select the friendly name of the certificate you created earlier in the "HTTPS certificate" drop-down list and click the "Apply" button.
For more details, you can refer to this link: https://askgarth.com/blog/how-to-setup-ssrs-to-use-https-part-2/.
If the answer is helpful, please click Accept Answer and Up-Vote for the same. If you have any questions, please feel free to let me know.
Best regards,
Aniya