Stripe connect hosted onboarding form allow sandbox connection

Hi, I’m trying to find out if Stripe connect hosted form in “testmode” is supporting sandbox oauth connection for Stripe accounts.

In the current way for testing purpose we use the Stripe hosted connect page to link Stripe accounts standard to our main account using testmode oauth setting on both sides. This shows the Stripe connect page in test mode and when selecting one of the stripe accounts to connect it will connect in testmode.

I do see on the hosted page also the “sandbox” in one of the accounts but reports on the page as

“This is a sandbox. Sandboxes cannot be connected to a live mode account.”

What seems to be incorrect as the whole hosted form loads in test mode status.

Any idea if Stripe connect in test mode can work with sandbox accounts to connect with on “client side” or what might cause this?