ArcGIS Open Data fails to assign group membership

[MariamKhayyat]

ArcGIS Open Data fails to assign group membership!

Despite that a  group has been created,

a site has been ceated, and the group has been selected in the site group manager, also the service that has been added was shared with the group, but the assign group membership gives the following error:

the service that has been added does not appear in the site preview.

What might be the issue here?

Notes:

- I used a free trial to test if the problem from my site, but its attitude is the same, furthermore, the group manager in a site in a free trial open a blank page.

- ArcGIS desktop and adaptor 10.6.1 were used in publishing the service.