fix: Handle new error message, remove devMode.

[paouvrard]

Description

• After the testnet protocol upgrade there is a new error message which prevents onboarding of Ethereum wallets.
• Remove devMode to use native 0x accounts.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Type of change.

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• FEATURE - a PR of this type introduces a new feature.
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• TEST - a PR of this type adds more tests.
• CHORE - a PR introduces other changes than the specified above.