fix: Post requests from the side frame were sent to wrong URL

[fsbraun]

Description

This PR fixes a regression introduced in #386

Related resources

• 386

• ...

Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.50%. Comparing base (f90c5b2) to head (0be7364). Report is 9 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #396 +/- ## ========================================== + Coverage 90.88% 91.50% +0.62% ========================================== Files 72 72 Lines 2546 2579 +33 Branches 361 368 +7 ========================================== + Hits 2314 2360 +46 + Misses 168 155 -13 Partials 64 64 ```

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