Connection between flanges with just one collar

[s.strat]

Hi. I am struggling to set up a connection bettween a collared loose plate flange and a slip on. The issue is that when i connect it adds 2 collars and i would only like one. When i have the collared flange and try to add the SO to the conn. i have teh following error message,

[h_eger]

Dear @s.strat ,

This connection should be configured as an asynchronous connection.

[s.strat]

Could you please be more explicit about it? the connection seems to work for 2 collared lap flanges but when i replace one with SO it does not connect. Thank you.