Authorize.net Invalid or Missing token in Sandbox mode

I am not sure if the is the right community to reach out for a question like this but I am trying to give a client a test of what using authorize.net would look like in there website for client booking. The API for authorize.net is being linked to Simplybook.me and I know the API information and key are correct but I keep getting a Invalid or Missing token error at the final checkout.(image attached below)

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Is this suppose to happen while in sandbox mode?