wp.setOptions of the XML-RPC API does not appear to work

I think you may be confusing the send and response data formats.

(The format you are specifying to send with is the response format.)

You probably need to just send the value as: 

array("users_can_register" => "1");

Related Posts:

  1. WordPress as XML-RPC client?
  2. How to enable wpautop for XMLRPC content
  3. Extending xml rpc – best practice
  4. How do I know if my site is using the xmlrpc.php file?
  5. XML-RPC: Add category to post data
  6. How Enable XML-RPC in WP 4.8.2
  7. XMLRPC and Underscored custom fields
  8. Creating post content from external web scraper via JSON or RPC
  9. wp.getUsers XML-RPC method is returning only 50 users, how can i get all the users
  10. xmlrpc.php Returning 405 Response Code
  11. Restrict access to xmlrpc.php
  12. Simply deleting XMLRPC file
  13. Storing an XML Response (Transient)?
  14. Problem with Create Post using metaWeblog.newPost or wp_insert_post
  15. Is it possible to change a blog’s theme through XML-RPC command? (and if so how?)
  16. How pull wordpress blog data using Blogger API using python
  17. Create a new post in wordpress with XML-RPC with the correct GUID?
  18. Working code example of PHP XML-RPC connex to site?
  19. Automated posting to wordpress from commandline or XMLRPC API on Dreamhost
  20. Posting via HTTP requests?
  21. Why is minimum_args protected?
  22. Multiple new posts using XML-RPC?
  23. Is it possible write, publish and edit posts with WordPress from console aka terminal?
  24. How to enable xmlrpc in WordPress 5?
  25. modify post meta data remotely without xmlrpc
  26. XMLRPC newPost post_content issue
  27. Can XMLRPC set show_on_front/page_on_front?
  28. Send an extra parameter with xml-rpc login?
  29. Is there any image size limit for wordpress xml-rpc?
  30. XML-RPC and $wpdb
  31. XMLRPC won’t connect?
  32. How to list updates using WordPress XML-RPC methods
  33. Is XML-RPC still a security risk?
  34. Get Post meta via XML-RPC using wp.getPost
  35. How to process shortcodes in XML-RPC
  36. “XML-RPC server accepts POST requests only” error message
  37. New post created with XML-RPC works fine but fails to assign category
  38. Tagging posts to custom taxonomies using XMLRPC in R
  39. Getting all posts from an XMLRPC request [duplicate]
  40. not well-formed (invalid token) at line 15, column 51, byte 720 when trying to parse XMLRPC call
  41. XML-RPC aplication blocked by the hosting
  42. Weblog clients cannot retrieve posts: An invalid hexadecimal character (0x7) was found in the element content of the document
  43. Using XML RPC to import data into WordPress
  44. Page content sent from XML RPC is corrupted
  45. metaWeblog.getRecentPosts is returning nothing in my iphone app
  46. tag is ignored when using xml-rpc
  47. How to read newpost return post ID value as integer for xmlrpc
  48. Enabling XML-RPC Accross 500 blogs
  49. Retrieve username and password from XMLRPC request
  50. XMLRPC System Multicall and BruteForce
  51. Fatal Error: Allowed Memory Size of 134217728 Bytes Exhausted (CodeIgniter + XML-RPC)
  52. SSO / authentication integration with external ‘directory service’
  53. How to validate XML-RPC post creation and cancel when needed?
  54. Is there a way to get protected meta fields through any of the available built-in WordPress APIs? (xmlrpc, wp-json)
  55. xmlrpc_enabled filter not called
  56. Set default custom post type for XML-RPC
  57. custom XMLRPC method plus authentication of user & WooCommerce order
  58. X-Pingback and XMLRPC
  59. wp.getUsersBlogs XMLRPC Brute Force Attack/Vulnerability
  60. Most efficient way to insert a post outside WordPress?
  61. Disable links in header (feeds and such)
  62. How to get all posts (in chunks) via XML-RPC?
  63. get total number of images from media using xml-rpc
  64. Best way for plugin to accept POSTs?
  65. Overwrite default XMLRPC function from plugin
  66. wordpress inserting posts programatically through a url
  67. Attach to wp-login.php and xmlrpc.php
  68. Help Me Choose RSS or XML-RPC
  69. WordPress can’t find IXR_Client
  70. XMLRPC filtering through htaccess not working
  71. Turn off Admin Bar (Toolbar) in backend – no easy way
  72. How to activate plugins for my WordPress sites from a remote server
  73. Checking post format during xmlrpc_publish_post
  74. Execute upgrade-theme with coding
  75. How to block XML-RPC attack?
  76. Multisite -> XMLRPC
  77. Remotely search WordPress sites using xml-rpc
  78. wp.getComments is returning nill, when i called from my iphone app [closed]
  79. How to edit feature image with XML RPC?
  80. Queries take 120+ seconds on my large WordPress site
  81. Checking for origin of a xmlrpc request
  82. Do I need to instantiate the XMLRPC class or any class in another class to access its methods?
  83. Using Microsift Word/Outlook for content publishing to WordPress
  84. Post via wp-admin and via iOS app, same hooks and triggers involved?
  85. Can I disable xml-rpc by setting it to false?
  86. Regular XML-RPC timeouts
  87. XMLRPC pingback.extensions.getPingbacks not work with parameters
  88. API WordPress is Limited? Return False
  89. Why none of xmlrpc filters work
  90. Insert custom post type via XML-RPC?
  91. Manage multiple wordpress installs (Best Practice)
  92. Anomaly with response coming from XML RPC Api get Post (integer out of range)
  93. Custom xmlrpc request does not pass parameters?
  94. Modifying WordPress XML-RPC Built-Ins
  95. Create a “feed” from one WordPress site to another?
  96. Getting the Posts’ permalinks from XLMRPC
  97. XMLRPC: How to retrieve possible custom fields for a new post?
  98. Disable XML-RPC via snippet
  99. XMLRPC error: xmlrpc.client.Fault:
  100. When accessing a wordpress blog, I want to force http when accessing wordpress via xmlrpc otherwise force https