Click on the <Xero Tax/Branding > tab followed by clicking on the button <Get Xero Tax Codes>
This will retrieve tax codes from your Xero Org
Update these <Xero Tax Codes> values highlighted in the image to <Opportunity Products> object custom field <Xero Tax Code> picklist.
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For Branding click on <Get Xero Branding Theme Id>
Update the custom field
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For Account Codes click on <Get Account Codes>
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