Granting SENDAS permission for a user on another account

Hello,

I have a question regarding SENDAS permission.

I have a client who owns 2 domains under 2 different Office 365 accounts.

Is it possible to make one user from one account SENDAS another from the second account?

I've done this before using powershell but only when all domains were under the same admin account.

This does not seem to work for me right now.

Any suggestions?

Thanks,

Gil