I had the same issue.
It resolved when I used the role SAP_SLD_CONFIGURATOR while configuring SLDAPICUST.
Maintained HTTP parameters as below:
Alias - SAP_CONFIG
Host Name - PI Host(Depends on how you configure your central SLD ours was PI)
Port -PI port
User - SLD_CL_SID(With above mentioned role.)
As said in above threads below RFC destinations of type T needs to be maintained.
SAPSLDAPI with registred program SAPSLDAPI_SID
LCRSAPRFC with registered program LCRSAPRFC_SID