Hi @roman_borodatov,
Thank you for your patience. For sandbox, following is the VCES iFrame URL:
https://vcescert.visammg.com/VCESIFrameSbx/?Token={1}&Lang={2}
So what you were using initially is correct. Please discard my previous reply.
Also in sandbox, you don't have the option to use your own redirect URL and CSS URL.
When you are ready to promote your project to the higher environment (CERT), you will be able to submit your own Common Redirect URL and CSS URL on the client onboarding form.
Hope this helps, please let me know if you have any other questions.
Best,
Stacey
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