Hello,
I can definitely say this is the issue you're encountering based on the Token id (tok_123) in your screenshot. The Token was created on one Stripe account in Test mode with the test Publishable key and then server-side your code tried to retrieve that Token on a different Stripe account.
Based on what I see, you seem to be using Stripe Connect but your server-side code is mis-configured. Your client-side application is creating a Token on a connected account that is connected to your platform. And then server-side, your code doesn't take Connect into account and tries to retrieve that token on the platform account. It fails since the token exists on the connected account instead. You are likely using the Direct Charges approach:
https://stripe.com/docs/connect/direct-charges
You need to change your code server-side to explicitly make the API request on behalf of the connected account. This is done by passing the `Stripe-Account` header set to the id of the connected account, which is the same one you configure client-side in your Flutter client. You seem to be using stripe-ruby so your code would be:
token = Stripe::Token.retrieve(
'tok_12345',
{stripe_account: 'acct_123'}
)
I do hope this unblocks you. I do think this is more a support question and less a fit on this mailing list at the moment. Make sure to reach out to our support team if you do have follow up questions about your integration and they will be able to help:
https://support.stripe.com/contact
Best,
Remi