Hello Yusuf,
Please check restgui service's setup is performed. Please complete this step and retest.
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Go to the handler list tab and change the handler from CL_HTTP_EXT_ITS to CL_HTTP_EXT_ITS_BASIC. If CL_HTTP_EXT_ITS_BASIChandler is not present, apply 1667055.
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Best regards,
Yuki