Purging with GYB purges the wrong mailbox

[mvmaastricht]

First of all a GREAT thank you to the GAM team for developing GYB! I'm using it to migrate emails of old nameless IMAP accounts from our provider (like hr@mydomain.com) to equivalent Google Groups in Google Workspace. I do that with a special account account I created for this: migrate@mydomain.com. I installed GYB from the admin account admin@mydomain.com. I want to use the following steps:

1. Import email from an external IMAP account into the migrate@mydomain.com Workspace account;
2. Use GYB to migrate the email from migrate@mydomain.com to the corresponding Google Group;
3. Use GYB to purge the migrate@mydomain.com account;
4. Start over with step 1.

However, the purge command wipes the admin account admin@mydomain.com in stead of the account migrate@mydomain.com...
I've use the following command:

gyb --email migrate@mydomain.com --action purge --use-admin admin@mydomain.com

What did I do wrong?

Oh, and by the way: if I use gyb --email migrate@mydomain.com --action purge --use-admin migrate@mydomain.com

I get:

Got 284 Message IDs                                                             

403: Insufficient Permission - insufficientPermissions

EDIT: in the meantime I discovered that I failed to give the right access to the migrate account (reading only). After revoking access from the account itself, I wasn't be able to regain access: kept on getting

ERROR: ('invalid_grant: Token has been expired or revoked.', {'error': 'invalid_grant', 'error_description': 'Token has been expired or revoked.'})

After trying lots of times, I deleted the migrate account completely and created a new migration account. After giving full access, I was able to purge with the command

gyb --email migrate@mydomain.com --action purge --use-admin migrate@mydomain.com

(so using --use-admin migrate@mydomain.com which is not the admin account...)

So my first question remains: why did GYB purge the admin account, while leaving the migrate account untouched?