employee synchronization with existing business partner (/SHCM/RH_SYNC_BUPA_EMPL_SINGLE)

[majidff_]

Hello Experts!

we use HR module in s/4hana itself (no success factor or ECC or any third-party system) so  each of personnel is already maintained in PA30. (including 105 info type for user ID)
on the other hand, those personnel are already defined as BP with general and supplier roles.
so we did not have any experience with new model of employee and business users.
everything works fine, but now , there's requirement for "business user" in some workflows in Fiori. what things should be done?
even we activate /SHCM/EE_BP_1 business function. was that necessary? 
the configuration for T77S0 is done. when use "/SHCM/RH_SYNC_BUPA_EMPL_SINGLE" to generate a new BP it works well.

but when we use that program to just make relationship between existing BP and employee with same code, the error raise that it is duplicated:

Business partner 467211 already exists - Synchronization failed.

in SLG1.

so the employee is there, with the same number BP already exist (with general and vendor role) , we just need to synchronize them to benefit from the concept of business user.

thanks.