R4R: Fix /txs/encode endpoint

[yangyanqing]

• Targeted PR against correct branch (see CONTRIBUTING.md)

closes: #4141
replace: 4147

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added a relevant changelog entry: sdkch add [section] [stanza] [message]
• rereviewed Files changed in the github PR explorer

---

For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #4212 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4212      +/-   ##
==========================================
+ Coverage   60.16%   60.17%   +0.01%     
==========================================
  Files         212      212              
  Lines       15188    15188              
==========================================
+ Hits         9138     9140       +2     
+ Misses       5421     5419       -2     
  Partials      629      629

[codecov]

Codecov Report

Merging #4212 into master will increase coverage by 1.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4212      +/-   ##
==========================================
+ Coverage   59.12%   60.17%   +1.05%     
==========================================
  Files         217      212       -5     
  Lines       14595    15188     +593     
==========================================
+ Hits         8629     9140     +511     
- Misses       5328     5419      +91     
+ Partials      638      629       -9

[alessio]

Please resolve the conflicts

[yangyanqing]

Done ! Thanks a lot for prompt. @alessio