Here is the Oanda customer service answer. It looks like some information is missing in the loop. What should we do? Ask for old compatible account or wait for an up to date plugin?

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Thank you for contacting OANDA.

Sounds like your project is built on the v1 REST API. Thus new users now only receive v20 accounts and can only be compatible with v20 REST API.

They must contact us and receive a legacy account to work with v1 REST API.

Regrettably we are in a transition period now, but in the future after you migrate your codes to v20 REST API things should be smoother.
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